Preheat the oven to 190C/375F/Gas 5. Line the bottom of an 8 to 10-inch tin with a piece of greaseproof paper. Butter the bottom and sides then dust with flour. Place the nuts into a food processor and whizz up until finely ground. Then add the chocolate and cocoa and whiz for 30 seconds to break up the chocolate. Remove to a bowl and set aside. Add the butter and sugar to the food processor and beat until pale and fluffy. At this point add the egg yolks 1 at a time them mix together with the chocolate and nuts.
In another bowl beat the egg whites with a pinch of salt until they form stiff peaks. Gently fold the egg whites into the chocolate, butter and nut mix. Pour all the mixture into the tin. Bake in a preheated oven about 1 hour. To test if the torte is cooked, insert a cocktail stick or the tip of a knife for 5 seconds; when removed it should be reasonably clean. Serve with whipped cream, ice-cream or creme fraiche.