Mirror Glaze Cake – GBBO Showstopper Challenge (Week 1)

IMG_4185So, who here watches The Great British Bake Off? I’m guessing everyone, right?

Well, as you probably know, the new series started last Wednesday and I could not be happier to have it back in my life again! I don’t know what it is about watching people bake a cake under pressure that makes millions of people turn on their television screens every week, but I’m not ashamed to say I’m one of them!

I’ve watched this show religiously since the beginning and have learned sooooo much about cake, biscuits and soggy bottoms over the years! It’s definitely helped me discover my love of baking, and this year I decided to up my baking game.

This year, I figured why not put myself in the bakers shoes and challenge myself to make the Showstopper Challenges from each episode? To the judges criteria, and in the given time limit. Because I clearly like to make things difficult for myself!

Therefore, each week I plan to write a post documenting my progress, whether successes… or failures…

This week’s Showstopper challenge saw the bakers making a ‘Mirror Glaze Cake’. You know the ones… those super shiny glazed cakes from all those sexy slow-mo pouring videos you’ll most definitely have seen all over the Internet. Yup, those ones. Kudos GBBO for being so on trend! *sassy hand emoji*
Now, I’d seen them all over Instagram, and kinda already knew what goes into making the glaze, but I’d never actually tried making one before. Instantly I didn’t think it would be too difficult, so naturally I decided to try and make something a bit fancier… because as I said, I like to make things difficult for myself.
galaxy5Lemon Genoise Sponge. Blackberry Buttercream. Fresh Blackberries. Galaxy Mirror Glaze. What’s not to love?
Though, to prepare myself for my OMG GALAXY MIRROR GLAZE CAKE, I decided I’d start off by practicing a mirror glaze before jumping into a galaxy far far away. I decided to test a recipe for a dark chocolate mirror glaze on a simple chocolate cake. The mirror glaze recipe I used was as follows:
  • 4 sheets of gelatine
  • 125ml water
  • 200g sugar
  • 150g chocolate
  • 60ml double cream
  • 30g cocoa powder

IMG_2131First I soaked the gelatine leaves in cold water.

IMG_4144Then I added the sugar and the 125ml of water to a large saucepan and left this to bubble until it reached 104°C. Once it reached this temperature I removed it from the heat.

IMG_4147To a large heatproof bowl I poured in the cream and snapped the dark chocolate into smaller pieces. I then poured the hot sugar on top, let sit for a minute then whisked thoroughly.

IMG_4149Finally, I sieved the cocoa powder into the mixture, and added the gelatine leaves (making sure to squeeze out any excess water) before whisking to combine.

IMG_4151To help everything melt/dissolve I also used a hand blender to blitz up any stubborn pieces of chocolate.

IMG_4152I even strained the glaze through a sieve to make sure it was completely smooth. So much effort, but totally worth it for such a sexy glaze!

IMG_4162I left the glaze to set up a little  (so it held it’s form for a few seconds when drizzling, and didn’t flow too quickly). Once I was happy with the consistency, I placed a small test chocolate cake on a tall container placed on a large baking tray (to catch all the glaze), before pouring the glaze over the cake in circular motions to coat the entire cake.



IMG_4166I then used a toothpick to pop any air bubbles for an even finish.

I let the cake set up a little before moving to the fridge to chill entirely.

IMG_4169Happy with my first attempt at a mirror glaze, I then attempted the GBBO challenge as stated in the episode:

  • Mirror Glaze
  • Genoise Sponge
  • 3hr time limit

IMG_2050I started with the lemon Genoise sponge, whisking the eggs and sugar till thick, pale and fluffy. This took a good 5 minutes ish.

IMG_2090IMG_2094I then sifted in the plain flour and added the salt and lemon zest. I gently folded this into the mixture, making sure there were no pockets of flour but trying not to stir out all of the air.

IMG_2096IMG_2085I squeezed the lemon juice into the cooled melted butter, then poured this into the cake batter and gently stirred to combine too.

IMG_2099 IMG_2100I poured this into a lined cake tin and baked at 180°C for 20-25 minutes until golden brown. (The cake should spring back slightly when pressed.)

IMG_2102For the blackberry buttercream, I started by whipping the butter until light and fluffy. This also took a good 5 minutes with an electric mixer.

IMG_2104I then sifted in the icing sugar and beat this together.

IMG_2113I blitzed up the fresh blackberries with a hand blender, then strained through a sieve to reserve the puree. (I yielded about 6tbsp.)

IMG_2118IMG_2119I added this to the buttercream, along with the milk and beat this together so the colour was evenly distributed.

IMG_2124Once the cake was cool, I levelled the top then sliced it in half.

I then frosted the cake with the buttercream (adding fresh blackberries to the centre). Applying a thin crumb coat to entire cake, I let this chill/set up in the fridge before frosting the entire cake. I left this to chill in the fridge completely whilst I made the glaze.

IMG_2140For the galaxy glaze, I made a white chocolate mirror glaze – so I could use food colouring to make the colours for the galaxy.

As before, I added the white chocolate and gelatine to the hot sugar (omitting the cocoa powder), blended, then strained through a sieve to get a smooth glaze.

IMG_2146 IMG_2151IMG_2153 IMG_2155I spooned about 5tbsp of glaze into two bowls each, and coloured those purple and pink. I then separated the rest of the glaze into 2 more bowls and coloured those black and navy.

I poured these onto the cake, mixing between the colours and swirling to create a galaxy pattern. I used a palette knife to gently smear across the cake to merge the colours together. I then left the cake to set up.

Once set, I mixed a little edible silver dust with a bit of water and flicked this onto the cake to create the stars.




How long did it take? I started at 11am and finished just after 2pm… so yup, about 3hrs. 😀 I even had time to do some washing up in between (not everyone has an endless supply of kitchen equipment at their disposal), take photos/videos. *hairflick* I mean, I did forget to take photos of a few stages… but we’ll overlook that. I certainly did.

What worked? The Genoise sponge, and the flavour combo. Win. Blackberries are so underrated!

What didn’t work? The food colouring I used wasn’t the greatest quality, so didn’t achieve the colour I wanted. Also, white chocolate is pretty temperamental… and I felt like the white chocolate glaze took a little longer to set to the right pouring consistency. Maybe chocolate quality?

Things to improve if I were to take this recipe to the tent? Maybe use a white food colouring first to achieve a brighter colour when adding the other colours? Test different brands of white chocolate too.


Mirror Glaze Cake – GBBO Showstopper Challenge (Week 1)
Author: Acorns & Custard
  • Lemon Genoise Sponge
  • 4 large eggs
  • 125g caster sugar
  • 125g plain flour
  • zest and juice of 1 lemon
  • 50g unsalted butter, melted and cooled
  • pinch of salt
  • Blackberry Buttercream
  • 300g unsalted butter, softened
  • 600g icing sugar
  • 150g fresh blackberries, plus a few extra for the middle
  • 2tbsp milk
  • Chocolate Mirror Glaze
  • 4 sheets gelatin
  • 125ml water
  • 200g caster sugar
  • 150g white/dark* chocolate
  • 60ml double cream
  • *additional 30g cocoa powder (if making dark chocolate glaze)
  1. Preheat oven to 180°C.
  2. In a large bowl, whisk the eggs and sugar for the sponge until thick, pale and fluffy. The mixture should be able to hold it’s form for a few seconds when drizzling – ‘ribbon stage’.
  3. Sift in the flour, salt and add the lemon zest.
  4. Gently fold into the mixture, making sure there are no pockets of flour but keeping as much air into the mixture as possible.
  5. Pour in the cooled melted butter and lemon juice and give one final (gentle) mix.
  6. Pour into a lined cake tin and bake for 20-25 minutes until the sponge is golden and springs back slightly when pressed.
  7. Leave to cool completely.
  8. Blitz up the blackberries in a food processor or blender till smooth. Strain through a sieve and reserve the puree. I yielded about 6tbsp.
  9. In another bowl, whip up the butter for a good 5 minutes until light and fluffy.
  10. Sift in the icing sugar and beat together.
  11. Add the blackberry puree and the milk and stir together so the purple colour is evenly mixed.
  12. Once the cake has cooled, level the top (if you wish), then slice in half along the middle.
  13. Place a bit of buttercream on the cake board you’re going to use, then place one of the cakes on top.
  14. Spread some of the butter cream on the first cake then scatter a few fresh blackberries on top.
  15. Place the second cake on top, then cover the whole cake with a thin layer of the buttercream. Place in the fridge and leave to chill – this is your crumb coat.
  16. Once the buttercream has set, cover the entire cake with the remaining buttercream as smooth and neat as possible. Leave to chill/set up in the fridge whilst you make the glaze.
  17. Soak the gelatine leaves in a small bowl of cold water.
  18. Roughly chop up the chocolate into smaller pieces.
  19. In a large saucepan, pour in the water and the caster sugar and heat till it reaches 104°C. Remove from the heat.
  20. Add the chocolate to the hot sugar mixture and carefully whisk to combine.
  21. Add the cream and whisk in too.
  22. Squeeze any excess water off the gelatine leaves, then add to the chocolate mixture and whisk in to combine.
  23. You may wish to use a hand blender to blitz up any smaller pieces of chocolate/gelatine.
  24. Leave to cool to about 20-30°C before pouring over the cake. The mirror glaze should have set enough that it won’t all run off, but runny enough that it doesn’t need to be coaxed down the cake.
  25. Place a tall glass/container on top of a large tray, then place the chilled cake on top of the glass. (This will catch the glaze as it drips off the cake.)
  26. Pour the glaze on top of the cake in circular motions, making sure to coats the entire cake.
  27. Leave to set up in the fridge for a few minutes. Cut off any drips, and serve.


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