Preheat the oven the 170°C/340F or 150°fan. Grease and line a 9"x13" (23cm x 33cm) rectangular cake tin.
Toss the vanilla extract and granulated instant coffee or espresso powder into the milk. The coffee will dissolve into the milk, making it easier to mix in with the rest of the ingredients.
Whisk together the flour, baking powder and salt. Set aside. Melt the butter and allow it to cool while moving on to the next step.
250 grams plain flour, 4 teaspoons baking powder, ½ teaspoon table salt
In a large mixing bowl beat the eggs and sugar until light and fluffy and has doubled in volume. About 3-5 minutes using an electric hand mixer/stand mixer.
3 eggs, 300 grams white granulated sugar
Pour the butter slowly down the side of the bowl with the mixer running. Mix until well combined. Similarly, add in the milk and mix through.
125 grams butter
Sieve the cocoa powder over the egg mixture. Add in half the flour and whisk together until just combined. Add in the rest of the flour and mix until just combined.
50 grams unsweetened cocoa powder
Pour the batter into the prepared baking tin. Smooth to the edges. Bake for 25 to 30 minutes or until a cake tester comes out clean from the centre of the cake. Cool in the tin for 10 minutes before turning out onto a cooling rack to completely cool.
While the cake is baking and cooling, heat up the cream either over medium heat in a small saucepan or in a heatproof bowl in the microwave.
Once the cream is hot and bubbling around the edges, toss in the blocks of chocolate. Allow the mixture to sit for 5 minutes, then whisk the mixture together until the ganache is smooth and creamy.
Allow the ganache to cool in the fridge, stirring it every 15 minutes to check on how much the ganache has set.
Once the ganache is set, meaning the ganache is firm yet still slightly stirrable. Beat the ganache either in a stand mixer or with an electric handheld mixture until the ganache has lightened in colour and is a bit fluffy.
Plop the frosting/icing over the top of the completely cooled cake, smooth until mostly even using an offset spatula or the back of a dessert spoon. Then create swirly patterns on the top if desired.
All temperatures stated are for conventional ovens. Decrease the temperature by 20°C/25°F or gas mark 1 for "fan" or air-fryers.
Notes
If you prefer less icing/frosting on the cake, simply half the ganache. You can use the little 0.5 buttons for ease!This recipe also makes about 18 regular sized cupcakes - simply reduce the baking time to 15-20 minutes. Or until a cake tester comes out clean. This recipe can also be used to make an 8" (20cm) 2-layer cake. Divide the batter between 2 greased and lined 8" round cake tins and bake for 20-25 minutes. Or until a cake tester comes out clean.