Preheat the oven to 425 F.
Place the peaches in a large mixing bowl and sprinkle with the lemon juice.
In a small mixing bowl, whisk together the sugar, cornstarch, and cinnamon. Toss the dry ingredients with the peaches. Spread the mixture in a 10 x 15-inch baking dish. Bake for 10 minutes.
To make the topping: In the bowl of a food processor, combine the flour, brown sugar, 2 tablespoons of the granulated sugar, baking powder, baking soda and salt. Add the butter and pulse to chop into small pea-sized pieces. Add the sour cream and pulse just until mixed.
Remove the peaches from the oven and drop the topping by large spoonful's onto the hot filling. Sprinkle the remaining 1 tablespoon granulated sugar over the topping. Bake for 15 to 18 minutes, until the filling is bubbling and the topping is golden brown. Serve warm.