Prepare the Filling: In a large mixing bowl, combine sliced peaches and chopped rhubarb. Sprinkle in granulated and brown sugars, cornstarch, optional spices, lemon juice, and vanilla extract. Toss gently with a spatula until all the fruit is evenly coated. Set aside.

Prepare the Pie Crust: Roll out one pie crust on a lightly floured surface until about 12 inches in diameter. Fit it into a 9-inch pie dish, trimming excess dough to leave a ½-inch overhang.

Fill the Crust: Spoon the fruity mixture into the prepared pie crust, ensuring it's distributed evenly. Dot the top with small pieces of butter.

Top the Pie: Roll out the second pie crust and lay it over the filled pie or cut into strips for a lattice design. Seal and cut slits if using a whole crust.

Bake the Pie: Preheat the oven to 375°F (190°C). Brush milk over the top and sprinkle sugar. Bake for 45-50 minutes until golden brown and bubbly.

Cool the Pie: Remove from oven and let cool on a wire rack for 1-2 hours to allow filling to set.