Creating the Brown Butter Strawberry Peach Pie is straightforward if you follow these steps:

1. Preheat the Oven: Preheat your oven to 375°F (190°C).
2. Brown the Butter: In a medium saucepan, melt the butter over medium heat. Continue cooking until it turns golden brown and releases a nutty aroma. Remove from heat and let it cool slightly.
3. Make the Crust: In a large bowl, combine the flour, salt, and granulated sugar. Pour in the browned butter and mix until crumbly. Add the egg and mix until a dough forms.
4. Chill the Dough: Shape the dough into a disk, wrap in plastic wrap, and refrigerate for at least 30 minutes.
5. Prepare the Filling: In a separate bowl, combine the strawberries, peaches, brown sugar, cornstarch, lemon juice, vanilla extract, and cinnamon (if using). Toss until the fruit is well coated.
6. Roll Out the Dough: On a floured surface, roll out the chilled dough to fit a 9-inch pie pan. Place the dough in the pan and trim the edges.
7. Fill the Pie: Pour the fruit mixture into the crust, spreading it evenly.
8. Bake the Pie: Bake in the preheated oven for 45-50 minutes, or until the filling is bubbling and the crust is golden brown.
9. Cool the Pie: Remove the pie from the oven and let it cool for at least 15-20 minutes before slicing.
10. Prepare Egg Wash: Brush the crust edges with milk for a beautiful finish before baking.

Following these steps will guide you in creating an incredible Brown Butter Strawberry Peach Pie that will impress your family and friends.