Begin by preparing your pie dough, and let it chill while you make the filling. Note: The pie dough has to chill for at least an hour before being rolled out. Take it out of the fridge 10 minutes prior to rolling.
Basic Pie Crust
To make the filling: place the apples, rhubarb, brown sugar, white sugar, cornstarch, and vanilla into a large mixing bowl. Mix until the fruit is well coated in the sugars.
2 large apples, 18 oz. rhubarb, ¼ cup brown sugar, ¼ cup white sugar, 2 tablespoons cornstarch, 1 teaspoon vanilla extract
Roll the first disc of pie dough out to fit your pie plate. Place the bottom crust into your pie dish and press gently to fit into the depth of the dish. Trim the edges with a sharp knife.
Add the rhubarb mixture to the pie plate, making a rough even layer.
Roll out the second disc of dough and place over top of the filling. Trim the edges again. Press the outer edge of the pie with a fork to seal the dough. Decorate as desired or make a lattice if you prefer.
Brush the crust evenly with the beaten egg, then sprinkle with coarse sugar.
1 large egg, Coarse sugar
Cut a few openings or slits in the top of the pie to let steam and any bubbling juices escape during baking. Place the pie into the refrigerator while you heat the oven, approximately 20 minutes.
Preheat oven to 375°F (190°C) and place a baking sheet (or sheet of tin foil) at the base of the oven to catch any drips that may bubble over.
Once the oven is hot, place pie onto the middle rack and bake for 60-65 minutes, or until very golden.
Remove the pie from the oven and cool completely before serving, at least 5-6 hours. Leftovers will keep well in a sealed container for up to 3 days, but it is best eaten on the first day.
Notes
The pie dough has to chill for at least an hour before being rolled out. Take it out of the fridge 10 minutes prior to rolling.Cool the pie completely before serving, at least 5-6 hours, to let the filling set.