Grease the pan, line the base with paper and grease the paper. Heat the oven to 300°F/150°C.
Grind the walnuts with the chocolate in two batches in a food processor or a few at a time in a blender. Alternatively, grind them with a rotary cheese grater.
Cream the butter with three-quarters of the sugar. Beat in the egg yolks, one by one, then stir in t