01 -
Warm the oven to 400°F (200°C). Lay one pie dough into each of your two 8-inch pie pans and push it down to fit snugly against the bottom and edges.
02 -
Toss the chopped rhubarb and 1/2 cup of sugar in a bowl that’s safe for the microwave. Heat on high for 4–5 minutes until the rhubarb turns soft and juices start collecting. Drain the liquid into a measuring cup and, if it’s not enough, add some water to reach 2 cups. Stir in cornstarch until it fully dissolves.
03 -
Pour 2 cups of the rhubarb liquid into a pot. Mix in the leftover sugar (1 cup), lemon juice, serviceberries, and softened rhubarb. Stir as it heats over medium-high until the mixture thickens and starts bubbling, roughly 5 minutes.
04 -
Split the filling evenly between the two pie shells. Cover both with the second crusts, cutting little vents on top. Press the edges together to keep everything secure.
05 -
Slide the pies into the oven preheated at 400°F (200°C) and bake for 15 minutes. Turn the temperature down to 350°F (175°C) and bake for another 30 minutes, or until the tops are golden and the filling peeks out in bubbly streams.