1. MAKE TOPPING: Mix flour, 1/2 cup white sugar and baking powder. Add milk and 1/4 cup butter. Stir until all lumps are gone. Set aside.
2. MAKE FILLING: In a medium saucepan, stir together brown sugar and cornstarch; add water. Add peaches and blueberries. Cook and stir gently over medium heat until bubbly. Add lemon juice and 1 tablespoon butter and stir until butter melts.
4. Pour in an ungreased baking dish and spoon mounds of topping over the hot filling. Sprinkle with mixture of remaining white sugar, nutmeg and cinnamon. To avoid spillover in the oven, place baking dish on top of a cookie sheet.
5. Bake cobbler in a 350-degree F. oven for 35 minutes or until a toothpick inserted in the crust comes out clean. Serve warm with ice cream, or if you are feeling frisky, whipped cream. If blueberries are not available, you can add one additional cup of peaches to the recipe.
NOTE: According to the author, Marilyn Schiveley, of Folsom, it's a "killer" because it's so good. "It's to die for," she said. "My aunt and uncle had a peach ranch in Colorado back in the 1950's, and this is a tried and true, never-fail recipe that gets rave reviews every time."