1. Make crust: In a food processor, pulse flour, granulated sugar, and salt until combined. Add butter and pulse until mixture resembles coarse meal, with a few pea-size pieces of butter remaining. With machine running, add 1 cup ice water. Pulse until dough is crumbly but holds together when squeezed; do not overmix. Divide dough into 2 disks, wrap each tightly in plastic, and refrigerate until firm, at least 1 hour (or up to overnight).

2. Preheat oven to 400 degrees. Make filling: In a large bowl, toss together strawberries, rhubarb, granulated sugar, light-brown sugar, tapioca, and orange zest and juice.

3. Lightly flour a work surface and rolling pin. Roll out 1 disk to a 12-by-16-inch rectangle. Transfer dough to a 10-by-14-inch jelly-roll pan. Press gently to fit into pan and fill with fruit mixture. Roll out remaining disk to an 11-by-15-inch rectangle. Place atop pie, pressing along edges to seal. Trim edges of dough, leaving 1 1/2-inch overhang all around. Fold overhang under, tucking it into pan. Crimp edges. Brush crust all over with egg-yolk mixture and sprinkle with sanding sugar, if desired.

4. With a paring knife, cut slits on top to vent. Place pie in oven, then reduce temperature to 375 degrees. Bake until crust is deep golden brown and juices are bubbling in center, 55 to 65 minutes. Let cool on a wire rack, 1 hour. Serve warm or at room temperature.