01 -
Heat your oven to 400°F (200°C). Push one pie crust down and around the sides of two 8-inch pie dishes.
02 -
Mix rhubarb with 1/2 cup sugar in a bowl that's safe for the microwave. Heat it until the rhubarb gets soft and makes juice at the bottom, about 4 to 5 minutes. Pour the juice into a measuring cup and top it off with water until you've got 2 cups. Stir in cornstarch until it's all mixed in.
03 -
Put your 2 cups of rhubarb juice in a pot. Throw in the other cup of sugar, lemon juice, serviceberries, and rhubarb. Cook it on medium-high until it gets thick and starts bubbling, around 5 minutes.
04 -
Split the filling between your two pie crusts. Cover each with the leftover crusts and poke some small holes on top. Squeeze the edges together to close them up.
05 -
Stick them in your hot oven at 400°F (200°C) for 15 minutes. Then turn it down to 350°F (175°C) and keep baking until the crusts turn golden and you see the filling bubbling, about 30 more minutes.