1.Preheat oven to 180°C(160°C fan-forced). Line a 6-hole texas or 12-hole standard muffin pan with paper cases.
2.Beat butter, vanilla, sugar and eggs in small bowl with electric mixer until light and fluffy. Stir in sifted flour and milk in two batches.
3.Divide mixture evenly among three bowls. Tint one mixture pink. Blend sifted cocoa with extra milk in cup; stir into another mixture. Leave third mixture plain.
4.Drop alternate spoonfuls of the mixtures into cases. Pull a skewer backwards and forwards through mixtures for a marbled effect; smooth surface.
5.Bake large cakes about 30 minutes, small cakes about 20 minutes. Turn cakes onto wire rack to cool.
6.Combine ingredients for rocky road topping in medium bowl.
7.Place topping on tops of cakes; drizzle with the melted chocolate melts.