I think we’ve talked here before about how much I love sheet cakes. It’s all the flavour of a layer cake, but just way, way more laid back. They are super easy to transport (you just take the whole pan with you), are the best for loading up with sprinkles, and, I don’t know about you, but I LOVE making the swirls with my little offset spatula. I could seriously do it all day - it’s so relaxing to me.
Today’s recipe is a chance for me to love on the sheet cake just a little more, with this double chocolate situation. There’s a chocolate olive oil sheet cake on the bottom - it’s rich and moist, but still has a lovely springy texture, and a depth of flavour from the olive oil in the recipe. I then topped it with a fave of mine - milk chocolate german buttercream. Chocolate has got to be one of my all time faves when it comes to German buttercream. Someone once described it as room temperature ice cream, which I think is really just the perfect description. The chocolate goes so nicely with the silky buttercream, giving you this smooth, decadent topping to the cake. This cake would go great with a load of different buttercreams - in fact, there are a heap on the site here for you, but I can’t go past a good double chocolate pairing, and sprinkles are optional but also kind of necessary.
A few wee tips:
- I used a milk chocolate in the buttercream, which gave a very light taste, but if you wanted something a bit darker, sub the milk chocolate for a good quality dark chocolate.
- Ideally the pastry cream for the German buttercream needs to chill down - I like leaving it for at least a few hours, or overnight if I can.
- This cake is great as it comes together all in the one bowl - you end up with quite a bit of mixture, so make sure that you have a big enough bowl!
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Answers to your baking questions
Over the years, many of you have asked me questions about:
- baking in grams
- adjusting oven temperatures
- what kind of salt to use
- and many more!
I've curated and answered them all for your easy reference in this frequently asked questions post!
Chocolate Olive Oil Sheet Cake with Milk Chocolate German Buttercream
- Yield: Makes one 9” x 12” cake - serves 12-16 people 1x
Description
Chocolate Olive Oil Sheet Cake with Milk Chocolate German Buttercream
Ingredients
Chocolate Olive Oil Cake
- 375g all-purpose flour
- 350g sugar
- 120g dutch cocoa
- 2 tsp espresso powder
- 1 tsp salt
- 1 ½ tsp baking soda
- 2 tsp baking powder
- 4 eggs, at room temperature
- 1 ½ tsp vanilla
- 180g extra virgin olive oil
- 330g whole milk, at room temperature
- 300g freshly boiled water
Milk Chocolate German Buttercream
- 110g sugar
- 12g (1 ½ Tbsp) cornstarch
- 1 egg
- 1 egg yolk
- 1 tsp kosher salt
- 190g whole milk
- 1 tsp vanilla bean paste
- 340g (3 sticks) unsalted butter, at room temperature
- 180g good quality milk chocolate, melted and cooled slightly
Instructions
CHOCOLATE OLIVE OIL SHEET CAKE
- Preheat the oven to 350°f / 180°c. Lightly spray a 9”x13” baking pan with baking spray, and line with parchment paper. Set aside.
- In a large bowl, whisk together the flour, sugar, cocoa, espresso powder, salt, baking soda, and baking powder. Add the eggs, vanilla bean paste, oil, and milk, and mix to combine well. Add the boiling water and whisk until incorporated.
- Transfer the batter into the prepared pan, and tap a few times on a flat surface to remove any excess bubbles.
- Bake the cake for 40-45 minutes, until the centre springs back, or a cake tester inserted in the middle of the cake comes out cleanly.
- Cool in the pan completely.
MILK CHOCOLATE GERMAN BUTTERCREAM
- In a bowl, whisk together the sugar, corn starch, egg, egg yolk and salt. In a medium saucepan, heat the milk and vanilla 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 container or bowl of a stand mixer and press some plastic wrap over the surface to avoid a skin from forming. Refrigerate until cold - at least four hours, preferably overnight. If you need to speed this process up, you can place the pastry cream in a bowl, then place the bowl in an ice bath. Stir frequently.
- Fit your mixer with the whisk attachment, and place the pastry cream in the bowl. Whip the mixture on medium until creamy and lump-free. Begin adding the butter, a few cubes at a time, until fully incorporated. It may look curdled at some point but just keep whipping - it will come together! Once the buttercream is homogenous, add the cooled melted milk chocolate and mix to incorporate.
ASSEMBLY
- Transfer the cake to a serving plate or board. Dump the milk chocolate buttercream onto the cake, and, using an offset spatula, spread over the cake, creating swirls in the buttercream. Add sprinkles if desired.
- Store leftovers in an airtight container in the fridge.
Comments
pili says
can i substitute the coco and esspresso for lemon juice to make a lemon cake
Erin says
No. Please don't do that. Look for a lemon cake recipe 🙂
Sarah says
Made this as a half recipe to reduce gluttony as it was a birthday cake for 2, and it was sooo good. Made it in a weird oval glass Pyrex dish (gamble!) and it was fine, kept as fresh as the day I baked it, for about 4 days, in the middle of high Summer. Will make again and again. Delicious!
Sarah says
I made this for my daughter’s birthday cake as chocolate cake was her request. I must say it’s not a favourite flavour cake of mine but HOLY MOLY this one was amazing!! The German buttercream icing makes it! It’s like a dreamy ice creamy texture! This cake was a hit! And lasted so long as so big!
Erin says
Ahhh so happy to hear you loved! I hope she had a happy bday! x
Allana says
I had never made a sheet cake before and did not realise how large it would be - which is perfect for gatherings/ birthdays. It was also very moist and delicious!
Libby says
What a fun twist on a chocolate cake. It's dense and moist as one would expect from an olive oil cake. What really makes it is the Chocolate German Buttercream. Amazing! The lightness of the buttercream pairs so nicely with the denseness of the cake making the whole thing perfectly balanced. I often find chocolate on chocolate overwhelming so this is quite a find for me. I split the recipe into a batch of cupcakes and two 8" rounds and everything turned out perfectly. Would make this again in its true sheet cake form in a heartbeat.
Carina says
This is the most delicious moist chocolate cake ever! The buttercream is a dream and literally tastes like melted chocolate ice cream. I'm not a fan of American buttercream so I was so excited to find out about German custard buttercream. My favourite thing about Erin's recipes are that they're in grams and detailed. I'm never second guessing anything as everything is always thoroughly explained. Such a joy of a baking site!
Greer Jacobs says
Hi! I'm in NZ too, and haven't come across espresso powder or that particular olive oil. Do you have suggestions for alternatives?
Erin Clarkson says
Hi! Regular olive oil will work (something good quality) and just instant coffee powder for the espresso!
Linda Soucy says
Can I substitute vanilla extract for paste? I don't feel like running out to store but I really want to make this! If I can substitute, would it be equal amount or a little more for flavor?
Erin Clarkson says
Yep same amount!
Rusha says
Hii, wanted to know whether I would need to adjust the temp by 20 degrees if I have a fan oven??
Erin Clarkson says
Hi! Yes, usually! If you have an oven thermometer that can be handy to know what temp you are working with.