1. Preheat oven to 170°C. Grease and line base and side of a 6cm deep, 22cm (base) round cake pan.
2. Place chocolate in a heatproof, microwave-safe bowl. Microwave, uncovered, on MEDIUM (50%) for 1 to 2 minutes, stirring every minute with a metal spoon, until almost melted. Stir until smooth. Set aside for 10 minutes to cool.
3. Using an electric mixer, cream butter, sugar and vanilla until light and fluffy. Add eggs, 1 at a time, beating after each addition. Add melted chocolate. Beat until well combined. Sift flour and cocoa together. Fold half the flour mixture into butter mixture. Add half the milk. Stir gently to combine. Repeat with remaining flour mixture and milk. Spoon into prepared pan. Smooth surface. Bake for 50 to 60 minutes or until a skewer inserted into the centre comes out clean.
4. Stand cake in pan for 15 minutes. Turn out onto a wire rack to cool completely. Spread icing over top and side. Top with chocolate curls, if using. Serve.
5. To make chocolate icing: Combine chocolate and cream in a heatproof, microwave-safe bowl. Microwave, uncovered, on MEDIUM-HIGH (70%) for 1 to 2 minutes, stirring every minute with a metal spoon, until almost melted. Stir until smooth. Set aside for 30 minutes or until thick enough to spread.
