Pre-heat oven to 400 F. Whisk together 1/3-2/3 cup sugar and 1 Tablespoon cornstarch. Peel, halve and pit 3 pounds of peaches, slicing them in 1/2" wedges into a 9" deep dish glass pie pan or bowl. Add 1 teaspoon lemon juice, 1 teaspoon vanilla, the sugar/cornstarch mixture and stir gently. Cover with foil and set aside.
Whisk together in a large bowl the flour, 1/4 cup sugar, and the baking powder, baking soda and salt. In a medium bowl, stir together the buttermilk and the chilled melted butter. Combine with the dry ingredients until just incorporated and the batter begins to pull away from the sides of the bowl.
Line a rimmed baking sheet with parchment paper. Using a greased 1/4 cup measure, scoop out and drop 8 mounds of dough onto prepared baking sheet, spaced about 1 1/2" apart. Combine 2 teaspoons sugar with 1/8 teaspoon ground cinnamon and sprinkle the mixture on top of the biscuits. Bake until puffed and lightly browned on the bottom, about 10 minutes. Remove from the oven and set aside.
Place the bowl of fruit in the oven and bake until the fruit is hot and has released its juices, about 20-25 minutes. Remove from oven, uncover and stir gently. Arrange the par-baked biscuits over the top and return to the oven. Bake until biscuits are golden brown and fruit is bubbling, about 15 minutes, rotating halfway through. Remove from oven. Let cool 15 minutes before serving. Serve warm.