Preheat oven to 180C.

Butter and flour 28cm spring form pan.

Carefully toast nuts in a dry frypan over moderate heat, then roughly chop.

Melt butter in a small saucepan, add chocolate and cocoa. Stir until smooth, remove from heat and cool.

Using electric beaters, whip egg whites to snowy peaks & set aside.

Use beaters to whip egg yolks, sugar and vanilla in a wide bowl until creamy.

Stir in flour, nuts and a pinch of salt.

Very gently fold in egg whites with a metal spoon.

Scrape into tin, bake for about 20-30 minutes until top is dry, but middle is still moist and soft.

Dust with icing sugar to serve.