Start by peeling, pitting, and slicing your peaches into even wedges. Toss them with cornstarch, flour, cinnamon, salt, allspice, maple syrup, bourbon, and vanilla extract. This ensures each slice is coated with a flavorful, slightly thickened syrup.
In a saucepan, melt the butter over medium heat until it turns golden brown and smells nutty. Stir in brown sugar, flour, chopped pecans, and a pinch of salt. Mix until crumbly but well combined. Set aside to cool slightly.
Roll out your pie crust into a 9-inch pan. Pour the peach filling into the crust and gently spread it evenly. Sprinkle the brown butter pecan streusel on top, covering the filling completely.
Place the pie in a preheated oven at 375°F (190°C) and bake for 45 minutes or until the streusel is golden brown and the filling is bubbling. Let the pie cool for at least 1 hour before slicing to allow the filling to set.