Preheat oven to 425°F.
Toss peaches with sugar, cinnamon, lemon juice, and cornstarch in a pyrex or glass baking dish and bake in middle of oven 10 minutes.
Make topping while peaches bake:
Stir together flour, sugar, baking powder, cinnamon and salt. Blend in butter with your fingertips or a pastry blender until mixture resembles coarse meal. Stir in water until just combined.
Remove peaches from oven and drop spoonfuls of topping over them. Bake in middle of oven until topping is golden, about 25 minutes. Topping will spread as it bakes.
Adapted from Gourmet, September 1999