Mint Slice Cake

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For my brother Christian’s 16th birthday, he requested a mint slice cake. That was weeks ago and I’ve been thinking about how to execute it ever since. I was tickled pink by his request as I have loved Arnott’s mint slice biscuits since the dawn of time and as a consequence of my deep abiding love for them I no longer permit myself to keep them in the house – ours is a deeply dysfunctional romance.

In the planning stages for this cake, I thought about just making Steph’s (of raspberri cupcakes fame) gorgeous Mint Slice Cake but for me, the best thing about a mint slice is the textural differences – the crunch of the biscuit, the smooth mint fondant and the glossy firm chocolate coating. Steph’s cake looked amazing, but I realized I didn’t want to just make a cake that looked like a biscuit – I wanted to try to replicate the texture of a Mint Slice, just on a larger scale.

For the base, I didn’t think a biscuit recipe would give me the proportional thickness or crunch that I wanted, and I knew a standard chocolate cake would be too fluffy. At first I planned to have a brownie base, but I decided against this as I didn’t want it to be too fudgy. Eventually I settled on a sort of macaron/meringue torte hybrid, as I reasoned it would have the crispness i was looking for but would also be substantial enough to support the fondant layer & ganache, particularly when sliced and served. I made the batter using a bastardized macaron method, but substituted hazelnut for almond meal as I felt it was more chocolate-y (perhaps a subliminal callback to my beloved Nutella?) and added some chopped chocolate to the batter as well. At the last minute I also threw in some coffee powder to make the chocolate really sing.

For the mint fondant layer, I used this simple peppermint cream recipe – just egg white, sugar and peppermint essence, with the quantities tweaked just a bit to get the proper soft texture. I initially had looked at a lot of buttercream recipes but was wary of the fact that buttercream often has a yellow/cream tint to it. I really wanted the peppermint filling to look exactly like the real thing, as white and clean as possible. Using raw egg whites isn’t for everyone, but I reasoned that there would be no pregnant, young, elderly or otherwise immunologically weakened people eating the cake, so I went with it! It turned out beautifully, with the same soft texture as you find in a real mint slice, and no oiliness.

The chocolate coating was the simplest thing to decide – I simply used a chocolate ganache, with a ratio of 2:1 chocolate to cream to encourage it to firm up when poured. I did at one point consider using tempered chocolate to get a perfect glossy crunchy finish, but I don’t own a candy thermometer and besides, there’s a limit to even my culinary perfectionism/insanity!

Recipe with detailed instructions after the jump…

Mint Slice Cake

Ingredients

For ‘biscuit’ cake base:
100g aged egg whites (I used fresh egg whites, microwaved at 40% power for 10 seconds)
110g hazelnut meal
190g pure icing sugar
60g dark chocolate
15g cocoa powder
1/2 tsp instant coffee powder
50g caster sugar

For peppermint fondant filling:
75g egg whites
500g pure icing sugar, sifted
1/2 teaspoon peppermint essence

For chocolate ganache:
200g dark chocolate, chopped
100g pure cream

Method

1. Preheat oven to 150 degrees Celsius. Line the bottom of an 8-inch springform cake tin with baking paper, but don’t grease it.

2. In a food processor, pulse chocolate until it is finely chopped. It will look like dirt. Delicious dirt. Add icing sugar and pulse to remove lumps. Add hazelnut meal, cocoa and instant coffee powder, and pulse a few times to combine. Remove to large mixing bowl. If you don’t have a food processor, combine all ingredients in a bowl & stir to mix. I would recommend that you sift the icing sugar and perhaps grate the chocolate.

3. In a separate bowl, beat the egg whites until soft peaks form. Gradually add the caster sugar and keep beating until it holds firm peaks.

4. Add the egg whites to the dry ingredients and fold decisively until the ingredients are totally combined. The batter should be fairly thick. Make sure you scrape up all dry ingredients from the bottom of the bowl.

5. Pour (or scrape) the batter into the prepared cake tin. Let sit for 15 minutes, then bake for 45 minutes.

6. Take the cake out of the oven (the top should be dry, shiny & hard – it may be cracked in places but don’t fret). Run a knife around the outside of the cake, carefully as the cake will be quite dry and brittle. Remove the outer ring of the springform pan, then return the cake (still sitting on the base part of the pan) to the oven. Turn the oven off & stick a wooden spoon in the oven door to keep it ajar. Leave the cake sitting in the cooling oven for 2 hours.

7. Make the peppermint fondant: in a large, clean bowl, beat the egg whites with a whisk until they are frothy. Add 400g of the icing sugar and the peppermint essence and stir with a wooden spoon until combined. Add more sugar as needed until you are happy with the texture.

8. Scrape out the fondant onto cling film which has been dusted with icing sugar, dust more icing sugar on the top, shape into a disc roughly the same size as the cake (I found it helped to use the outer ring of the springform pan as a guide), cover with cling film & let rest at room temperature until you are ready to use it.

9. Assembly – remove the cake from the base of the springform pan & carefully peel off the baking paper. Set the cake, right side up, on a cooling rack set over a plate (to catch drips). Carefully unwrap the peppermint fondant & place on top of the cake, pressing & shaping until the top is only slightly domed. You do not need to press the fondant down over the sides of the cake – just let it sit on top. If the fondant is sticking to your hands too much, dust them with a little icing sugar.

10. Prepare the ganache: in a microwave safe jug (such as Pyrex), combine the chocolate and cream. Microwave on full power in 20 or 30 second bursts, stirring in between until all the chocolate has melted. I was careless in this step and my ganache ended up lumpy from bits of unmelted chocolate, so kids, don’t do what Donna Don’t did!

11. When the ganache is smooth and glossy, carefully pour it over the cake, guiding it with an offset spatula as necessary.

12. Let the cake sit at room temperature for half an hour so the ganache has a chance to set slightly, before transferring to a board or plate. I have found in the past that ganache does funky things in the fridge, so I prefer to store cakes frosted in it at room temperature, inverting a bowl over the cake to protect it as it sits on my kitchen bench. If you are organized enough to have a fancy glass cake cover-upper, this would be the perfect time to break it out.

So there you have it! A delicious mint slice cake.

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