Preheat oven to 350°F. Make topping: Combine the flour, sugar, baking powder, baking soda and salt in a medium bowl. Add the butter and work it into the dough with your fingers until the mixture resembles coarse crumbs. Stir in the sour cream and heavy cream. Coarsely chop 3/4 cup of the walnuts and stir them in. Roll the dough on a flat, floured surface to about 1 inch in thickness. Use a round cutter about 2 inches in diameter to cut as many circles as possible. Refrigerate the dough.
Make the filling and bake the cobbler: Toss 3 pints of the raspberries with the sugar, cornstarch, the lemon juice and half of the lemon zest. Pour half of them into a 10-inch cast iron skillet or a 9 by 9-inch baking dish and top with the 1/2 cup of walnuts. Top with the remaining raspberry mixture. Place the biscuit circles over the raspberries. Bake until the topping is golden brown and the juices have thickened, about 45-50 minutes. The biscuit top should be browned and fully cooked. Cool. In a small bowl, combine the remaining 1/2 pint raspberries, and remaining 1/4 cup walnuts and lemon zest. Top with the raspberry walnut mixture just before serving for added fresh flavor and crunch!