To create this incredible Brown Butter Strawberry Peach Pie, follow these simple steps:

1. Preheat Oven: Begin by preheating your oven to 375°F (190°C).
2. Brown the Butter: In a saucepan, melt the butter over medium heat. Stir continuously until it turns golden brown and smells nutty. Remove it from the heat and let it cool slightly.
3. Make the Dough: In a bowl, combine the flour, granulated sugar, brown sugar, salt, baking powder, and baking soda. Whisk well. Add the browned butter, egg, and vanilla extract. Mix until combined.
4. Chill the Dough: Form the dough into a disk, wrap it in plastic wrap, and refrigerate for about 30 minutes.
5. Prepare the Filling: In a large mixing bowl, combine the sliced strawberries and peaches. Add lemon juice, cornstarch, and a pinch of salt. Toss gently until well combined.
6. Roll out the Dough: After chilling, roll out 2/3 of the dough on a floured surface into a 12-inch circle to fit a 9-inch pie pan.
7. Assemble the Pie: Place the rolled-out dough into the pie pan. Pour the fruit filling over the crust.
8. Top the Pie: Roll out the remaining dough and cut it into strips to create a lattice on top of the pie. Alternatively, you can cover the filling fully with another crust and cut slits for venting.
9. Brush and Sprinkle: Brush the top with milk and sprinkle coarse sugar evenly over the crust.
10. Bake: Place the pie in the preheated oven and bake for 45-50 minutes or until the crust is golden and the filling is bubbly.
11. Cool: Once baked, remove from the oven and allow to cool for 20-30 minutes before serving.

Following these steps will guide you toward creating a stunning pie that showcases the delightful flavors of brown butter, strawberries, and peaches.