Preheat the oven to 425°F (220°C). Roll out the pie crust and fit it into the pie dish.

Trim and crimp the edges of the crust as desired.

In a mixing bowl, combine the cherries, blueberries, sugar, cornstarch, lemon juice, vanilla extract, and salt. Toss gently to coat the fruit.

Pour the fruit mixture into the prepared pie crust and dot with butter.

Cover the pie with a top crust or lattice, and brush the top with beaten egg. Sprinkle with sugar.

Bake in the preheated oven for 40-45 minutes, or until the crust is golden brown and the filling is bubbly.

Let the pie cool for at least 30 minutes before slicing.