Chocolate and Hazelnut Mousse Cake
Ingredients

200g (7oz) unsalted butter, cut into cubes
450g (1lb) dark chocolate, roughly chopped 
50g (2oz) hazelnuts, plus extra to decorate
50g (2oz) gluten-free plain flour (or just plain flour), sifted
10 large free-range eggs, separated
75g (3oz) caster sugar
mixed berries, to decorate
you will need
20cm (8in) cake tin, greased and the bases and sides greased and lined with baking parchment
Preparation

Heat the oven to 170C, 150C fan, 325F, gas 3. In a heavy-based saucepan melt the butter and chocolate over a medium low heat, set aside to cool.
Grind the hazelnuts until very fine using a food processor, mix with the flour and set aside.
Using an electric mixer, whisk the egg yolks with the sugar until thick and creamy. Gently mix in the cooled chocolate mixture using a hand whisk. In a separate bowl using an electric mixer, whisk the egg whites until stiff. Using a hand whisk fold in around a third to the chocolate mixture to loosen then carefully fold in the rest. When almost combined fold in the flour and hazelnuts. Spoon into the prepared tin and bake for 35-50 minutes. The cake will have fondant centre after 35-40 minutes or will be quite firm and mousse-like after 50 minutes. 
Remove from the oven and cover with a clean tea towel, allow to cool. Decorate with seasonal berries or chocolates and chopped hazelnuts to serve.