1. In a large bowl, toss the cherries, rhubarb, sugar, cornstarch, salt, and vanilla. Let sit for 10 minutes while you prepare the crust.

2. Whisk flour, sugar, and salt in a large bowl. Toss in the grated frozen butter and coat quickly with flour.

3. Drizzle the ice water-vinegar mixture one tablespoon at a time, stirring with a fork just until the dough holds together when pinched.

4. Divide the dough in half, shape into discs, wrap tightly, and chill for at least 1 hour.

5. Move an oven rack to the lowest position and preheat to 400°F. Place a foil-lined baking sheet on the rack.

6. Roll one dough disc on a floured surface into a 12-inch circle. Fit into a 9-inch pie plate without stretching. Trim the overhang to 1 inch.

7. Pour the rested cherry-rhubarb filling into the bottom crust, scraping every bit of juice from the bowl.

8. Roll the second disc into a 12-inch circle. Lay it over the filling, or cut strips for a lattice. Trim, fold the edges under, and crimp.

9. Brush the top with milk or beaten egg, then sprinkle with coarse sugar. Cut 4-5 steam vents if using a full top crust.

10. Place the pie directly on the hot baking sheet. Bake for 20 minutes, then rotate and reduce heat to 375°F. Bake another 25-30 minutes until the crust is deep golden and the filling bubbles thickly through the vents.

11. Check for doneness: the internal temperature should hit 200°F in the center. If the edges brown too fast, tent them with foil.

12. Cool on a wire rack for at least 3 hours before slicing to allow the filling to set.