Method

1. Heat oven to 190C/fan 170C/gas 5. Butter a 23cm spring-sided cake tin, then line the bottom with baking parchment and butter that as well. Tip 1 tsp cocoa powder into the tin, then tip and turn it so that the bottom and sides get covered in a fine layer. Tip out any cocoa that doesn’t stick.

2. Put the eggs and sugar into a large bowl and whisk with an electric hand beater for about 5 mins until very thick and pale. Pour the butter in around the edge of the bowl, then sieve in the flour and 4 tbsp cocoa powder. Fold in with a large metal spoon, cutting rather than mixing so that you preserve the bubbles. Pour into the tin and bake for 20 mins or until risen and springy. Cool for 5 mins in the tin, then turn onto a wire rack to cool completely.

3. Get ahead with the chocolate sauce. Put all the ingredients into a microwave-proof bowl and cook on High for 1 min or until the chocolate has melted. Stir briefly until smooth, then cover and set aside. Keep for up to 3 days or freeze for up to 1 month.

4. Once the cake is cold, take the ice cream out of the freezer to soften just a little. Cut the cake in half across the middle (the easiest way is to use a bread knife) and put the bottom onto a serving plate. Scoop one tub of ice cream onto the base in an even layer and top with half the crumbled Flake and half the hazelnuts. Top with the other half of cake, then cover that with scoops from the second tub of ice cream and the chocolate and nuts. Serve straight away with the sauce, or freeze for up to 1 month (see Know-how, below).

5. If you’ve frozen the sauce, take it out to defrost at room temperature a few hrs before serving. Transfer the cake to the fridge 1 hr before you want to serve it. If your chocolate sauce is still a little set, warm it for a few secs in the microwave on Low. Drizzle some of the chocolate sauce over the cake and serve with more in a little jug for pouring.