Pastry:
1 1/2 cup flour
1/2 cup cocoa
1/2 teaspoon salt
1 cup butter
1/3 cup sour cream

Filling:
16 ounces semi-sweet chocolate
1/2 cup cream
1//2 cup butter
5 egg yolks
1 teaspoon vanilla

To prepare the pastry, sift the flour, cocoa and salt together into a bowl. Cut the butter into the flour mixture with a pastry blender or two knives until resembles coarse meal. Add the sour cream and knead into a ball. Divide into 4 equal pieces and refrigerate 2 hours. on a floured board, roll each piece of dough out to a 10 x 10 inch square. Place each square on a buttered baking sheet. Prick all over and bake at 400 degrees for 10 minutes. Carefully transfer the pastry squares to racks to cool. They will be very fragile.

To prepare the filling, place the chocolate, cream and butter in a saucepan and stir over low heat until the chocolate and butter are melted. In a bowl, beat the egg yolks until thick and creamy. Beat in a few tablespoons of the hot chocolate mixture and stir back into the hot chocolate. Continue adding the chocolate to the eggs, beating well to keep the eggs from solidfying from the hot chocolate mixture. Stir in the vanilla and the the mixture cool to spreading consistency.

Do no refrigerate or it will be too stiff to spread. Place 1 pastry layer on a serving plate and spread with the filling. Continue layering and put filling on top.