Heat the oven. Set to 400°F (200°C). Place a rack in the lower third of the oven. Put a foil-lined baking sheet on the rack to catch drips.
Prep the crust. Fit the chilled pie crust into a 9-inch pie dish.
Crimp the edges. Prick the bottom lightly with a fork. Chill while you prepare the filling and crumble.
Make the fruit filling. In a large bowl, toss peaches and raspberries with sugar, cornstarch, lemon juice, vanilla, almond extract, and salt.
Let sit 10 minutes to start releasing juices. If the fruit looks very wet, add another 1 teaspoon cornstarch.
Stir up the crumble. In another bowl, combine flour, oats, brown sugar, cinnamon, and salt. Cut in the cold butter with a pastry cutter or your fingertips until it forms moist clumps.
Mix in nuts if using. The texture should hold when squeezed but still crumble apart.
Assemble the pie. Brush the crust edge with egg wash if you like. Spoon the fruit and all the juices into the crust.
Sprinkle the crumble evenly over the top, breaking up any very large clumps.
Bake hot, then lower the heat. Bake at 400°F for 20 minutes. Reduce heat to 350°F (175°C) and bake 30–40 minutes more, until the filling is bubbling in the center and the crumble is deep golden. If the edges brown too fast, cover the rim with foil.
Cool completely. Set the pie on a rack and let it cool at least 3 hours.
This helps the juices thicken so your slices hold together.
Serve. Slice with a sharp knife. Serve warm or at room temperature. Add vanilla ice cream, whipped cream, or a drizzle of heavy cream for extra comfort.