2 ½ cups all-purpose flour, plus a little extra for dusting dough and work surface
1 teaspoon salt
2 tablespoons sugar
12 tablespoons unsalted butter, chilled, cut into ¼-inch pieces
8 tablespoons all-vegetable shortening, chilled
6-8 tablespoons ice water
Mix flour, salt, and sugar. Using a food processor fitted with a steel blade, or using a pastry cutter, cut the butter into the flour. Add shortening, continuing to cut into the flour until the flour is pale yellow and looks like coarse cornmeal.
Sprinkle 6 tablespoons of the water over the mixture. Using a rubber spatula, fold the mix to work in the water. Press down on dough with broad side of spatula until dough sticks together, adding up to 2 tablespoons of water if needed to help the dough come together if needed. Divide into 2 balls, flattening each into a disk about an inch thick. Dust lightly with flour, wrap in plastic, and chill for ½ hour.
3 1/2 cups 1/2-inch-thick slices trimmed rhubarb (1 1/2 pounds untrimmed)
1 16-ounce container strawberries, hulled, halved (about 3 1/2 cups)
1/2 cup (packed) golden brown sugar
1/2 cup sugar
1/4 cup cornstarch
1 teaspoon ground cinnamon
1/4 teaspoon salt
Mix ingredients for filling and set aside.
Preheat oven to 400°F.
Roll out 1 dough disk on floured work surface to 13-inch round. Transfer to 9-inch-diameter pie dish. Trim excess dough, leaving 3/4-inch overhang.
Roll out second dough disk on lightly floured surface to 13-inch round. Cut into fourteen 1/2-inch-wide strips. Spoon filling into crust. Arrange 7 dough strips atop filling, spacing evenly. Form lattice by placing remaining dough strips in opposite direction atop filling. Trim ends of dough strips even with overhang of bottom crust. Fold strip ends and overhang under, pressing to seal. Crimp edges decoratively.
Blend 1 large egg yolk with 1 teaspoon water for glaze. Brush the exposed lattice.
Place the pie pan on a baking sheet and place in oven. After 20 minutes at 400°F, reduce temperature to 350°F, and continue baking for 1 hour and 25 minutes.