Preheat oven to 450ºF (204ºC).
In a large mixing bowl gently toss sliced peaches (5 cups) and lemon juice (1 tablespoon). Pour the peaches into a colander to drain for about 10-15 minutes. Pour drained peaches into a large bowl.
On a lightly floured counter, roll one pie crust into 12-inch circle. Place rolled crust in a 9-inch pie plate. Brush the bottom and sides of the crust (with a pastry brush) with beaten egg. Place in the fridge while you prepare the filling.
In a small mixing bowl whisk together flour (1/4 cup), cornstarch (3 tablespoons), sugar (1 cup), cinnamon (3/4 teaspoon), and nutmeg (1/4 teaspoon) until evenly combined.
Pour the flour/cornstarch mixture over the drained peaches and, using a large rubber spatula, gently intil peaches are evenly coated.
Remove the pie crust from the fridge and pour the peach mixture into the pan. Dot with small cubes of butter.
Arrange the top crust over peaches and flute or crimp together. Using a pastry brush, brush the entire top with heavy cream (2 tablespoons). Sprinkle with coarse sugar. Place on a rimmed cookie sheet to catch any drips.
Bake in preheated oven for 15 minutes. Reduce the heat to 350ºF (177ºC) and continue to bake for 25-30 minutes. Check halfway through the baking time to be sure the crust isn't browning too quickly. If it is, simply loosely cover it, with a piece of aluminum to shield the top.
Cool completely on a baker's rack, then refrigerate it for a couple of hours before cutting.