Heat the oven to 375°F. Put 1 cup of the flour, 6 tablespoons of the butter, and the salt in a medium bowl; blend with a pastry cutter or your fingers until the mixture resembles coarse crumbs. Add 2 tablespoons cold water and stir until the mixture forms a ball. (If the mixture is too crumbly, add an additional 1 tablespoon cold water.) Wrap the dough in plastic wrap and refrigerate while you prepare the filling and topping.

If you’re using fresh peaches, bring a large pot of water to a boil. Cut a small X in the flower (non-stem) end of each peach. Add the peaches to the boiling water and cook for 1 minute, then remove and rinse with cold water. Peel and slice the peaches.

Put the peaches, raspberries, powdered sugar, and lemon juice in a large bowl with ¼ cup of the flour and ½ teaspoon of the cinnamon. Stir gently to combine.

Put the oats, brown sugar, and pecans in a medium bowl with the remaining ¼ cup flour, 6 tablespoons butter, and ½ teaspoon cinnamon. Blend with a pastry cutter or your fingers until the mixture resembles coarse crumbs.

Unwrap the dough and place it on a lightly floured surface. With a rolling pin, roll out the dough until it’s approximately 11 inches in diameter. Transfer the dough to a 9-inch pie plate; trim any dough that hangs over the edges of the plate and discard the scraps. Transfer the peach mixture to the crust, and sprinkle the oat mixture over the peach mixture. Bake the pie until the topping and edges are golden brown, 40 to 45 minutes. Serve warm or at room temperature. (Store leftover pie in an airtight container in the refrigerator for up to a few days.)