Chocolate hearts can be made up to five days ahead. Cake can be made up to three days ahead. Keep, covered, separately in the fridge.
200g block dark cooking chocolate, chopped
125g unsalted butter, chopped
4 eggs, at room temperature, separated
1⁄2 cup caster sugar
1 cup hazelnut meal
Raspberries, halved strawberries and icing sugar mixture, to decorate
Double cream, to serve
1⁄4 cup White Choc Melts (50g)
Invert base of a 20cm springform pan (base measuring 18cm). Grease and line base and side with baking paper, extending paper 2cm above pan edge.
Place chocolate and butter in a large heatproof bowl. Sit bowl over a saucepan of simmering water. Stir until melted and smooth. Remove from heat. Cool completely.
Beat yolks and sugar in a small bowl of an electric mixer until pale and creamy. Add to chocolate mixture with hazelnut meal. Fold gently to combine.
Beat egg whites in same clean bowl of electric mixer until soft peaks form. Fold into chocolate mixture in two batches until just combined. Pour into prepared pan.
Cook in a moderately slow oven (160C) for about 50 minutes, or until a skewer inserted into the centre comes out clean. Remove from oven. Cool completely in pan. To make hearts, line a tray with baking paper. Melt chocolate in a heatproof bowl, sitting over a saucepan of simmering water, stirring until smooth. Pour onto prepared tray. Quickly spread to about 1⁄2cm thickness. Stand at room temperature until set. Using a 41⁄2cm heart-shaped cutter, cut out shapes. Gently lift off paper with a palette knife.
Decorate cake with berries, chocolate hearts and sifted icing sugar. Serve with cream.