Grease 2 x 8" sandwich tins, dust with flour and line base with parchment
Set oven to 375ºF, gas 5
Whisk egg whites until stiff and then gradually beat in the castor sugar
Continue beating until very stiff then mix in the vinegar and vanilla essence
Foldin the ground hazelnuts
Divide between the 2 tins and bake for 30 to 40 mins
Fill with chocolate cream and serve with the chocolate sauce from the next recipe.