
Heat oven to 350 degrees F. Lightly butter or oil a 9-inch square baking dish (or 2-quart dish).
Toss sliced peaches with berries (optional), lemon juice, sugar, 2 tablespoons of flour, cinnamon, nutmeg, and the salt. Pour into baking dish. Bake for 10 minutes.
Whisk flour, 2 tablespoons of sugar, baking powder and the salt together. Using a pastry blender or your fingers, cut butter into the flour until crumbly. Pour in milk. Stir with a fork until a soft dough forms. Dot tablespoon-sized dollops of biscuit dough over pre-baked peaches, leaving some space between each dollop. (As the cobbler bakes, the topping will spread out a little).
Combine the remaining tablespoon of sugar and cinnamon for topping. Sprinkle over biscuit dollops.
Bake the cobbler 40 to 50 minutes or until juices are bubbling and topping is golden brown. Cool 10 to 15 minutes before serving.