PREHEAT THE OVEN TO 450F. Combine the flour, baking powder and salt in a large mixing bowl. Cut in the vegetable shortening using a pastry blender or two knives until the mixture has the consistency of coarse crumbs. Add the milk, adding more milk if necessary so the dough is pliable but is still wet. Turn the dough onto a heavily floured surface, and knead it lightly (8 to 10 times). Do not overwork the dough. Roll the dough into a rectangle 1/3-inch thick. Mix the melted butter with the brown sugar, cinnamon and nuts. Press the mixture into one half of the dough, then fold the dough over to encase the filling, pressing it lightly to adhere. Cut out biscuits with a 2-inch round cutter (the diameter of a juice can), dipping the cutter in flour between cutting each biscuit so they do not stick. Place the biscuits on an ungreased cookie sheet and bake in the center of the oven for 12 to 15 minutes, or until golden brown. Serve immediately, or bake up to 2 hours in advance and reheat for 5 minutes in a 300F oven. Makes 12 to 14. These biscuits are delicious served warm with sweet butter or apple butter.