Butter the baking dish and preheat the oven to 425F. In a large bowl, toss together gently the berries, sugar, cornstarch, lemon juice and lemon rind. Let the mixture stand for 15 minutes. Arrange the mixture in the baking dish and dot it with the butter. Into a bowl sift tougher the flour, sugar, baking powder, baking soda and salt. Add the butter and the shortening and blend the mixture until it resembles coarse meal. Stir in the buttermilk and form the dough into a ball. On a floured surface press the dough gently into a round, 1/2 thick and with a 2 inch round cutter. Stamp out rounds then gather the scraps together and form into biscuits. Arrange biscuits over berry mixture. Brush dough with the egg glaze and bake the cobbler in the middle of the oven for 30 minutes, or until the biscuits are pale golden and the filling is bubbling. Serve the cobbler warm. Posted to the BBQ List by Carey Starzinger on Mar 27, 1996.