Rich Chocolate Brownie sheet cake is finished with a chocolate hazelnut German buttercream. German buttercream is pastry cream based, and is the perfect accompaniment to the rich, fudgy brownie cake.
Hi hi! Back with another Valentines-ish recipe - a chocolate brownie sheet cake with chocolate hazelnut buttercream. I recently made this for a friend’s birthday party - I often take cakes to parties, and sheet cakes are now my go-to because of how easy they are to transport and serve. There’s no worrying about a stacked cake falling over or getting damaged, and squares of cake with frosting on top are much easier to serve than a full layer cake. Both have their place, but for ease of transport etc, sheet cakes are the the best!
I riffed on an older recipe of mine and turned this brownie layer cake into a sheet cake. The brownie is slightly more cakey than a traditional fudgy brownie, because I needed it to have a little structure, but still retained that rich chocolate taste that we all love from a brownie, with a moist texture thanks to the butter and oil in the recipe.
The brownie bakes up nice and flat, which makes it perfect sheet cake material. I finished it off with one of my all time favourite things - German buttercream, to which I added a healthy dose of chocolate hazelnut spread to to make the most silky luscious buttercream that paired so well with the dense brownie cake. The chocolate hazelnut spread added the most amazing depth of flavour - Deb from Smitten Kitchen once described German buttercream as “room temperature ice cream” and I can’t agree more. Make it. It’s just the best ever.
My friend who had the birthday is a huge Friends fan, so I added some lobster themed sprinkles, which were the perfect way to finish off a cake. The sprinkles are actually Valentine’s themed, but seeing as her birthday is late Jan, we killed two birds with one stone. This cake was eaten off napkins in a Lower East side oyster bar, and it went down an absolute treat.
A few wee tips:
- This makes a BIG cake. You can make a half batch and bake it in a 9” square pan.
- I don’t have any cut shots of this sorry as it was a birthday cake for a friend - so I tested everything a few days before and then re made and shot the cake on the day of the party!
- The brownie cake needs to be totally cool when you frost it, so make sure that you give it enough time to cool before you add the icing.
- The pastry cream for the German buttercream also needs time to cool before you incorporate the butter - I like to make it ahead if I can and just pop it into a container, but if you are really in a pinch then you can spread it onto a quarter sheet pan and place plastic wrap directly on the surface of the pastry cream (don’t skip this step or you will get a skin on your custard and it’s not cute), and then cool it in the fridge in the sheet pan - the larger surface area will mean that it cools quickly. Alternatively you can place it into a metal bowl and make yourself an ice bath situation, stirring often to help distribute the pastry cream to help it cool evenly.
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Answers to your baking questions
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Chocolate Brownie Sheet Cake with Chocolate Hazelnut German Buttercream
- Prep Time: 45 minutes
- Cook Time: 45 minutes
- Total Time: 1 hour 30 minutes plus chilling time
- Yield: Serves 18-24 1x
Description
Rich Chocolate Brownie sheet cake is finished with a chocolate hazelnut German buttercream. German buttercream is pastry cream based, and is the perfect accompaniment to the rich, fudgy brownie cake.
Ingredients
Chocolate Brownie Sheet Cake
- 190g unsalted butter, cold from the fridge, cut into chunks
- 375g dark chocolate (I used 72%), chopped
- 300g granulated sugar
- 200g dark brown sugar
- 7 eggs, at room temperature
- 1 tsp vanilla bean paste or vanilla extract
- 210g neutral oil
- 150g all-purpose flour
- 150g dutch process cocoa
- 1 ⅛ tsp baking powder
- 1 tsp kosher salt
Chocolate Hazelnut German Buttercream
- 110g granulated sugar
- 12g corn starch
- 1 egg yolk
- 1 egg
- 1 tsp salt
- 1 tsp vanilla bean paste
- 190g whole milk
- 340g unsalted butter, at room temperature
- 320g chocolate hazelnut spread (I used Pan di Stelle)
- Sprinkles to finish (optional)
Instructions
CHOCOLATE BROWNIE SHEET CAKE
- Preheat the oven to 350° / 180°. Grease and line a 9”x13” baking pan with parchment paper.
- In a small saucepan over medium heat, heat the butter and chocolate, stirring constantly, until melted and combined. Set aside to cool.
- In a small bowl, whisk together the flour, cocoa powder, baking powder, and salt.
- In a large bowl, whisk together the sugar, dark brown sugar, eggs, vanilla, and oil. Add the cooled chocolate mixture, and mix to combine. Add the dry ingredients, and gently fold to combine.
- Transfer the batter to the prepared baking pan and bang on the counter once or twice to help it settle.
- Bake for 45 to 50 minutes, checking for doneness after 45 minutes, until a the top of the cake is set, and skewer inserted in the middle of the cake comes out with a few crumbs attached.
- Allow to cool completely in the baking pan.
CHOCOLATE HAZELNUT GERMAN BUTTERCREAM
- In a bowl, whisk together the sugar and corn starch, then add the egg, egg yolk and salt, and whisk together well. In a medium non-stick saucepan, heat the milk and vanilla bean paste to just shy of a simmer. Remove from the heat.
- Using one hand to whisk constantly, pour half of the hot milk mixture into the egg mixture. This helps to temper the eggs and stop them from scrambling. Whisk until incorporated, and then pour the whole lot back into the saucepan.
- Heat the milk and egg mixture over medium heat, whisking constantly, until it begins to bubble. It will thicken quickly. Once it has thickened, cook for one minute, then remove from the heat. Pour into a shallow dish or bowl of a stand mixer and press some plastic wrap over the surface to avoid a skin from forming. Refrigerate until cold.
- If you are in a hurry, you can speed up this process by placing the custard mixture into a bowl, and placing the bowl into an ice bath, stirring frequently.
- Fit your mixer with the whisk attachment. Whip the custard mixture on medium until creamy and lump-free. Begin adding the butter, a few cubes at a time, until fully incorporated.
- Add in the chocolate hazelnut spread, and whip until smooth, then whip for a further 2-3 minutes until light and fluffy. Switch to the paddle attachment and beat on low for 3-4 minutes to help remove any big air bubbles.
ASSEMBLY
- Carefully remove the cooled cake from the pan - I do this by turning it onto a wire rack, then using another wire rack with parchment paper on top to flip it up the right way - alternatively you can also put the buttercream on while it is still in the pan, which makes it super easy to transport.
- Scrape the buttercream onto the cake, and spread using an offset spatula - swoop it on as desired. Finish with sprinkles if using.
- Store leftovers in an airtight container at room temperature or the fridge.
Keywords: brownie cake, sheet cake, nutella, chocolate hazelnut, german buttercream, chocolate, brownie
Comments
Made this for a friends birthday and WOW!! Best German buttercream I have ever made. Not sure I can ever go back to regular buttercream!
★★★★★
Hi, how high the sides of the 9x13 pan used in this recipe? I’m looking at buying a pan this size (in NZ), and the height of the sides varies. Thanks!
Hi! I think it is 2.25" (5.7cm) high! It's a USA pan 9x13 🙂
Super easy recipe to follow and perfect!
★★★★★
This looks amazing! I am always wanting chocolate cake to richer, so a "brownie cake" sounds like a fun thing to try. Also, do you have any thoughts on if this would work well frozen, as the base for an ice cream cake?
Hi! I think it might, but it would be super dense? I would be more inclined to use my regular brownie recipe as it's more fudgy than a cake and freezes really well without going rock hard