Preheat oven to 400 degrees F (200 degrees C).

Combine 1/2 cup sugar, cornstarch, and cinnamon in a saucepan and whisk to mix. Stir in sliced peaches and lemon juice, tossing until peaches are evenly coated.

Cook filling over medium heat, stirring constantly, until mixture thickens and boils. Boil 1 minute. Pour mixture into an ungreased 2-quart casserole dish. Keep mixture hot in oven while you make the topping.

In a medium bowl, combine flour, 1 tablespoon sugar, baking powder, and salt. Mix thoroughly, then cut in shortening until mixture looks like fine crumbs. Add milk and stir until mixture is evenly moistened.

Remove peach filling from oven and drop dough onto peaches in 6 equal-size spoonfuls.