Make the filling first. Melt the butter in a medium saucepan over medium heat. Add the diced apple, golden raisins, sugar, cinnamon, and nutmeg. Stir everything together and cook for 6 to 8 minutes, stirring occasionally, until the apple is tender and the mixture smells fragrant. You want the apple soft but not mushy.

In a small bowl, stir the cornstarch into the cold water until dissolved, then pour it into the pan. Stir and cook for 1 to 2 more minutes until the filling thickens and looks glossy. Spread the filling onto a plate or shallow bowl and let it cool to room temperature before you fill the pies. Hot filling will make the dough greasy.

Preheat your oven to 400 degrees F and line a baking sheet with parchment paper. Let the refrigerated pie dough sit at room temperature for about 10 minutes so it unrolls without cracking. Unroll both rounds on a lightly floured surface and use a 3.5 to 4 inch round cutter or the rim of a wide glass to cut circles. You should get about 8 circles per round, 16 total.

Place 8 of the circles on the prepared baking sheet, spaced about an inch apart. Spoon a heaping tablespoon of cooled apple raisin filling into the center of each circle, keeping a clean border around the edge. Do not overfill or the pies will burst at the seams.

Brush the border of each filled circle lightly with egg wash. Lay a second dough circle on top of each one and press the edges together firmly with your fingers. Then press all the way around with the tines of a fork to seal and crimp. Use a small knife or skewer to poke 2 or 3 small slits in the top of each pie so steam can escape.

Brush the tops of all the pies with egg wash and sprinkle with coarse sugar if using. Bake for 18 to 22 minutes until the pies are deep golden brown. Let them cool on the pan for at least 10 minutes before eating. The filling will be very hot right out of the oven.