Place an oven rack in the center of the oven, then preheat to 375°F. Wash and dry the fresh produce. Halve, pit, and thinly slice the peaches. Halve the lemon crosswise; squeeze the juice into a bowl, straining out the seeds. In a large nonstick pan, heat 1/4 of the butter on medium-high until melted. Add the sliced peaches, lemon juice (carefully, as the liquid may splatter), half the sugar, and a pinch of salt. Cook, stirring occasionally, 8 to 10 minutes, or until softened. Turn off the heat. Stir in the blueberries, flour, and vanilla powder until thoroughly combined.

Melt 2/3 of the remaining butter (you will have extra) in a large bowl in the microwave (or melt in a small pot on the stove, then transfer to a large bowl). Add the cornbread mix and remaining sugar; stir until the mixture resembles wet sand.

Place the pie crust on a sheet pan, leaving it in its tin. Transfer the filling to the crust, then evenly top with the cornmeal crumble. Bake 30 minutes, or until the crumble and crust are golden brown and the filling is bubbly. Remove from the oven and let stand at least 15 minutes before serving. Enjoy!