More like whoopee pies - these babies are cause for celebration!
For the pastry cream:
1 1/2 cups milk
4 egg yolks
1/4 cup caster (super-fine) sugar
1/8 cup flour
2 tbsp cornstarch
1/2 tsp vanilla extract
For the whoopie cakes:
1 box vanilla cake mix
3 1/3 tbsp oil
2 3/4 tbsp water
For the ganache:
5 oz dark chocolate
2/3 cup heavy cream
Let's get Cooking...
Make the pastry cream: In a saucepan, add the milk and bring to a boil. Remove from heat and let it cool for a few minutes.
In a large mixing bowl, add the eggs and sugar and whisk together. Add the flour, cornstarch and vanilla and mix to combine. Pour in the hot milk and stir to combine. Return the mixture to the saucepan over low heat, whisking constantly, while bringing it to a boil. Cook until thickened, then remove from heat and transfer mixture to a bowl. Put plastic wrap on the surface of the pastry cream to stop it forming a skin, and chill until needed.
Make the whoopie cakes: Preheat the oven to 350 degrees.
In a mixing bowl, add the cake mix, eggs, oil and water and whisk together. Transfer batter to a piping bag fitted with a 1/2-inch round nozzle, and pipe 1 1/2-inch rounds onto a tray. Bake for 15 minutes, then leave to cool on a wire rack.
Make the ganache: Finely chop the chocolate and place in a large mixing bowl. Warm the cream in a saucepan until it comes to a gentle simmer, then pour it over the chocolate and whisk into a smooth, shiny ganache.
Assemble: Sandwich the cakes together with piped pastry cream, then spoon ganache over the top. Drizzle runnels over the side of the cakes, just like a Boston Cream Pie. Leave to set in the fridge for one hour, then serve.