Dark Chocolate Gateau with Coffee Buttercream and Roast Chestnuts

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Ingredients:

Chocolate and Coffee Sponge Cake

  • 6 Eggs (yolk and white separated)
  • 100g Sugar
  • 125g Brown Sugar
  • 125g All Purpose Flour (sifted)
  • 25g Cocoa Powder (sifted)
  • 7g Baking Powder (sifted)
  • 2g Salt
  • 50g Unsalted Butter
  • 1tbsp White Wine Vinegar
  • 1tbsp Vanilla Extract
  • 70ml Coffee

Coffee Buttercream and Roast Chestnuts Filling

  • 9 Egg Yolks
  • 225g Sugar
  • 200ml Coffee
  • 50ml Alcohol (Rum, Amaretto, Whisky, Bourbon or Brandy)
  • 250g Unsalted Butter (diced, and at room temperature)
  • 2g Salt
  • 100g Roast Chestnuts (chopped)

Dark Chocolate Ganache and Almond Topping

  • 75g Dark Chocolate
  • 100ml Heavy Cream
  • 25g Butter
  • 50g Slivered Almonds (toasted)

Instructions

Chocolate and Coffee Sponge Cake

  1. Preheat the oven to 350ºF.
  2. Grease a sheet pan (18inch x 13inch) all over with butter, and line the base of the sheet pan with non-stick parchment paper and apply another coating of butter on top.
  3. Pour your flour, cocoa powder and baking powder into a bowl and stir until well combined.  Set aside.
  4. In a bowl of a stand mixer, add your egg whites, salt and vinegar and whisk under medium high speed for 1-2mins until foamy.  Add your sugar, and continue whisking for approximately 5-6mins on high speed until you’ve reached stiff peaks and the meringue becomes glossy and smooth.  Using a rubber spatula, remove your meringue from the stand mixer bowl and set it aside in another bowl.
  5. Add your egg yolks, brown sugar and vanilla into your stand mixer bowl and whisk under medium speed for 2-3mins until thoroughly combined and foamy.
  6. Add all your dry ingredients into your egg yolk mixture a third at a time.  Between each interval of your dry ingredients, add half your coffee to your egg yolk mixture.  Whisk under low speed until just combined, and scrape the bottom and sides of the bowl with a rubber spatula before each new addition of wet and dry ingredients.
  7. Add 1/3 of your meringue into your chocolate and egg mixture and fold it in until well combined, before gently folding in the remaining 2/3 of your meringue.
  8. Pour your cake mixture into your baking sheet and spread it evenly across the surface.  Place it in the oven and bake for approximately 20mins until cooked.
  9. When ready, remove and set aside.

Coffee Buttercream and Chestnut Filling

  1. Place your egg yolks and alcohol into a bowl of a stand mixer and whisk for 2-3mins under medium speed until light and foamy.
  2. Place your coffee and sugar into a pan and cook under medium high heat until it reaches 250ºF and becomes a thick syrup.
  3. Begin whisking your egg yolk mixture again under low speed and slowly pour all your coffee sugar syrup into your egg yolks in a thin steady stream.  After you’ve added all your coffee syrup, turn up the speed of your stand mixer to high and continue whisking.
  4. After 2-3mins of whisking your egg yolk mixture, reduce your mixing speed and slowly start adding your butter and continue to whisk.  After you’ve added all your butter to your mixture, continue to whisk for another 1-2mins until your coffee buttercream mixture has cooled down and stabilized.
  5. Add your roast chestnuts and gently fold it into your coffee buttercream mixture.
  6. Remove and set aside in another bowl.

Dark Chocolate Ganache

  1. In a pan, add your heavy cream nd cook over medium low heat until the mixture comes to a simmer.
  2. Add your chocolate and butter, and stir until all your chocolate is melted and thoroughly combined.

Assembly

  1. Remove your chocolate and coffee sponge from your sheet pan.  Cut in half length ways to give you two equal sized rectangular sheets of cake.
  2. Add your coffee buttercream mixture on top of one of your cake sheets, spreading it evenly across the entire surface.
  3. Place your other cake sheet on top of the other one with the buttercream and chestnut filling.  So you have your two cake sheets on top and bottom with your coffee buttercream and chestnut mixture sandwiched between them.
  4. Pour your dark chocolate ganache on top of your cake, spreading it evenly across the entire top surface of your cake.  Garnish the top by sprinkling with slivered almonds.
  5. Place in the refrigerator and allow to chill and set for 3-4hours until your coffee buttercream mixture is set firm.
  6. Remove your cake from the fridge and trimmed off the edges to clean up the presentation.

Notes

  • This is a sweet decadent dessert, that’s great especially on the holidays when you’re looking for a show stopper!  The combination of chocolate, coffee, chestnuts and almonds work exceedingly well together, producing a fantastic end result that’ll completely satisfy anyone with a sweet tooth. 
  • This is a dessert that’s recommended you make a couple of days ahead.  So it’s ideal when you’re planning a large meal or function and want something extravagant to serve that’s ready and waiting for you.
  • I know on first appearance, this recipe is a bit disorienting but it’s really not that difficult.  You can break it up in stages to help manage the workload.  For example, you can make the dark chocolate and coffee sponge cake a day in advance to lessen the workload a bit, instead of doing it all in one day.
  • A good tip when beating eggs, is to use room temperature eggs versus eggs that are straight out of the fridge and stone cold.  The reason being that eggs that are room temperature are easier to whip and produce more volume.
  • When folding in the meringue into the cake mixture, the first 1/3 that you add you can be aggressive and vigorously stir it into the cake mixture to lighten it before gently adding and folding in the remaining 2/3 of the meringue.  The reason being you want to ensure the cake mixture is light and uniform enough to take the remaining 2/3 of the meringue without the risk of deflating it.   
  • When making your coffee buttercream mixture, it’s important that you don’t add your butter till early.  Otherwise the residual heat from your sugar syrup mixture might cause the butter to split as you’re adding it in.  It’s also important to add your butter slowly and gradually, otherwise it might split again.
  • A bit of a cheat is to use store bought roast chestnuts to save you a bit of time and effort.   

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