Mix all cake ingredients in a food processor for 5 minutes.
Pour into a 26cm cake tin and bake at 160°C for 45 minutes.
Cool the cake in the tin for 10 minutes before moving to a cooling rack.
Cream the topping ingredients until smooth and spread over the cooled cake.
Whisk egg yolks and sugar for the ice cream until white and stiff.
Boil milk, milk powder, and cream together in a saucepan.
Whisk the hot milk mixture into the eggs and return to the heat.
Cook the mixture to 80°C, sieve it, and stir in the melted white chocolate.
Process in an ice cream machine and store in the freezer until serving.