Step 1

Preheat your oven to 180C/160C Fan and line a 9x13" Traybake tin with parchment paper.

Step 2

Beat together your butter and sugar until light and fluffy.

Step 3

Add in the eggs, self raising flour, cocoa powder and vanilla extract and beat again until combined well.

Step 4

Pour into the tin and bake in the oven for 45-50 minutes, or until baked through.

Step 5

Once baked, let the cake cool fully in the tin.

Step 6

Add the icing sugar and cocoa powder to a medium sized bowl, and gradually add the water, mixing well each time, until a thick icing paste is made.

Step 7

Carefully spread the icing over the cake evenly.

Step 8

Sprinkle over your favourite chocolate sprinkles!

Step 9

Add the egg yolks, sugar, and flour to a large pan and whisk until smooth. Start to heat the egg yolk mixture on a low heat

Step 10

Pour in the milk gradually whilst whisking, and pour in the vanilla extract

Step 11

Whilst whisking continuously, heat the mixture to a simmer and let it simmer for several minutes until it starts to thicken

Step 12

Once starting to thicken, add the milk chocolate and dark chocolate and let this melt whilst still stiring

Step 13

Continue to heat the custard until you reach your desired consistency

Step 14

Serve with the cake immediately if you want it hot, or let it cool for cold custard!