1. Preheat oven to 180°C/160°C fan forced. Invert the base of a 23cm round springform pan (22cm base). Grease and line the base and sides with baking paper, extending the paper 2cm above the rim.
2. Place chocolate in a microwave safe bowl. Microwave on medium temperature for 1-2 minutes. Stir until melted. Set aside to cool slightly.  
3. Beat butter, sugar and vanilla in the bowl of an electric mixer with paddle attachment until pale and creamy. Add eggs, one at a time, beating between additions. Stir in melted chocolate.
4. Combine the flour and cocoa in a sieve. Sift half over the batter, then add half the milk and stir until smooth. Repeat with the remaining flour and cocoa mixture and milk, stirring until smooth. Pour mixture into prepared pan. Bake for 50-55 minutes or until a skewer comes out clean.
5. Cool in pan for 30 minutes, then release the pan from the  sides of the cake leaving the paper intact. Allow cake to cool. This can be done overnight.

Mousse

1. Sprinkle gelatine over hot water in a microwave safe jug. Stir with a fork. Microwave for 10 seconds on high. Stir until completely dissolved. Set aside to cool slightly.
2. Place eggs, hot milk, cocoa, sugar, vanilla extract and gelatine mixture in the jug of a high-speed blender. Blend until completely smooth and velvety. Transfer to a bowl. Fold in whipped cream. Place in the fridge for around 45 minutes or until thick enough to spread but not set firm.
3. Return the cake to the springform cake pan and clip back in place. If paper has come loose, rejoin with spray oil (see tips). Stir mousse until smooth. Spread on top of cake. Return to fridge for 4 hours or overnight until set. 

Chocolate Cream Frosting 

1. Whisk cream, icing sugar and cacao in the bowl of an electric mixer until soft peaks form. Add mascarpone and beat just until firm peaks form, around 30 seconds. Do not overbeat or cream will separate.
2. Remove cake from pan and transfer to a cake stand. Remove paper carefully.
3. Reserve 2 cups of chocolate cream for piping. Spread remaining chocolate cream around the sides and on top, smoothing the surface.
4. Fit two piping bags, one with a 1.5cm star nozzle and the other with a 1.5cm plain round nozzle. Fill each with 1 cup of the reserved frosting. Pipe rosettes and dots in varying sizes around the top of the cake to form a wreath. Decorate with Easter eggs and edible flowers, if using.
5. Refrigerate until ready to serve. Remove cake from the fridge 20 minutes before serving.