1Pre-heat the oven to 180C/160C Fan/Gas 4. Grease an ovenproof 1L pudding basin. Line the base with baking paper.
2Put 115g butter, 115g caster sugar, 2 eggs, 115g flour and 1/2tsp baking powder in a bowl. Beat for 2-3 minutes with an electric hand-whisk, until pale and fluffy. Set aside.
3In another bowl, beat the 60g butter, 60g sugar, 1 egg, 40g flour and 1/2 level tsp baking powder, plus 25g cocoa powder and 1 tbsp milk.
4Put alternate spoonfuls of the two mixtures in the pudding basin. Level the surface. Bake for 45-55 minutes, until risen. To check if it's ready, insert a skewer into the centre; it should come out clean.
5Cool in the basin on a wire rack for 15 minutes. Turn out and leave to cool completely.
6 Beat the remaining butter, icing sugar and milk together, to make a fluffy buttercream.
7Stand the marble cake sponge, rounded-side up, on a cake board. Use a knife to cut out 3 ice-cream cone-size holes. Cut off both ends of the cone, then push the remaining middle piece into the holes to make bunny warrens.
8Spread the buttercream over the cake and board.
9Mix the coconut with the green colouring. Sprinkle on the cake and press in with the fat side of a knife.
10Mix the remaining icing sugar with water, to make a stiff icing, then dab on 7 of the larger marshmallows to make bunny cheeks. Use the cake decorations to make noses and eyes.
11Using scissors, cut 14 slices from the other 2 larger marshmallows, for ears. Paint a pink stripe down the centre of each, then stick on the bunnies.
12Use icing to stick on mini marshmallow tails.
13Arrange the bunnies and sugar flowers on the cake.