Plum Peachy Pie

Preheat oven to 425°F. Place half the plums and peaches in a heavy saucepan. Place remaining fruit in a bowl. Add lemon zest, brown sugar, salt, tapioca starch, nutmeg, and cinnamon to pan. Mix and let sit for about 10 minutes to draw out juices. Bring to a gentle boil over medium heat until juices begin to thicken. Remove from heat and pour over uncooked fruit. Stir in lemon juice and set aside to cool. Place one crust in a shallow, nine-inch glass pie dish, allowing pastry to hang over the edge. Pour in fruit filling. Cover with top crust. With kitchen scissors, neatly cut edge leaving one inch of overhang around rim. Carefully fold edge under and crimp to seal. Cut a half-inch circle in the middle of pie crust and several slits. (Re-roll scraps and cut out shapes to decorate the top.) Beat egg and milk together and brush over top, then sprinkle with sugar. Cook on a baking sheet for 15 minutes until  top begins to golden, then reduce heat to 375°F and continue to bake about 30 minutes, or until pastry is golden brown and the filling bubbles in the middle. Cool for one hour.