- Preheat oven to 180°C (350°F/Gas 4).
- Lightly grease and flour a 4-cup (1 litre) capacity heart-shaped cake tin or silicone mould.
- Sift 185 g plain (all-purpose) flour, 1 teaspoon baking powder, 3/4 cup (145 g) caster (superfine) sugar and 1/4 cup (30 g) unsweetened cocoa powder into a medium bowl and mix until well combined.
- Add 125 g melted butter, 2 eggs, 3/4 cup (180 ml) milk and 1 teaspoon vanilla extract, and whisk until smooth.
- Pour into prepared cake tin or mould.
- Bake for 1 hour, or until cooked – a skewer inserted in the centre will come out clean.
- Cool cake in tin on wire rack for 10 minutes, then turn out to finish cooling. If in a mould, cool completely in the mould before turning out.
- Cover with buttercream (see below).
- Beat 125g softened unsalted butter until light and creamy.
- Gradually beat in 1 cup (125 g) icing sugar and continue beating until the mixture is light and fluffy.
- Add 125g melted and slightly cooled dark chocolate and beat until combined.
- Spread over cake and allow to set.