Preheat oven to 180 degrees C. Butter and flour 8 mini cakes moulds or a muffin tin.
In a large clean bowl, beat egg whites with an electric mixer until stiff peaks form, adding the icing sugar a bit at the time as you mix. Sift in the flour and mix gently. Stir in ricotta, baking powder, walnuts and chocolate.
Divide the cake mixture evenly into 8 prepared moulds or muffin tin.
Bake in the preheated oven for 35 to 40 minutes or until a skewer inserted into the middle of one comes out clean.