Pre-heat oven to 375 degrees.
In a large bowl gently toss the raspberries, peaches, sugar, cornstarch, cinnamon and salt.
Let sit while you prepare your crust.
Line your pie tin with your first crust and keep it in the refrigerator while you make the lattice topping.
Make a lattice topping with your second crust.
Add the fruit filling to the pie plate.
Cover with the lattice crust then fold the edges of the lattice topping under the back of the bottom layer of pie crust and pinch them together to seal them together.
Beat egg and milk together and brush it onto the pie crust.
Sprinkle coarse sanding sugar over the top pie crust.
Bake at 375 degrees for 30 minutes then at 350 degrees for an additional 30 minutes.
If your pie is browning too quickly tent it lightly with a piece of foil to prevent additional browning (do not remove it from the oven sooner).
Cool pie before slicing so the filling can thicken.