1. Combine strawberries, rhubarb, cornstarch, 2 Tbsp. sugar, and 1 1/2 tsp. orange zest in a small bowl.
2. Preheat oven to 375°. Combine flour, salt, and remaining 1/4 cup sugar in a large bowl. Cut in butter and shortening with a pastry blender until mixture resembles small peas. Stir in remaining 1 1/2 tsp. orange zest. Drizzle with ice-cold water and orange juice. Stir with a fork until combined. (Mixture will be crumbly and dry.) Knead mixture lightly, and shape dough into a disk. Divide dough in half.
3. Roll half of dough to 1/8-inch thickness on a heavily floured surface. (Cover remaining dough with plastic wrap.) Cut with a 2 1/4-inch round cutter, rerolling scraps as needed. Place half of dough rounds 2 inches apart on a parchment paper-lined baking sheets. Top with 1 rounded teaspoonful strawberry mixture. Dampen edges of dough with water, and top with remaining dough rounds, pressing edges to seal. Crimp edges with a fork, and cut a slit in top of each round for steam to escape. Repeat procedure with remaining dough and strawberry mixture.
4. Stir together egg yolk and cream; brush pies with egg wash. Sprinkle with sugar. Freeze pies 10 minutes.
5. Bake at 375° for 20 to 25 minutes or until lightly browned. Cool 10 minutes. Serve warm or at room temperature. Store in an airtight container up to 2 days.