Flaky Crust
3 cups all-purpose flour
2 1/2 teaspoons granulated sugar
3/4 teaspoon salt
2/3 cup chilled solid vegetable
    shortening, cut into pieces
1/2 cup plus 2 tablespoon chilled unsalted
    butter, cut into pieces
About 10 tablespoon ice water

Combine flour, sugar and salt in a food processor or blender. Using the pulse feature, cut in shortening and butter until a coarse meal forms. Blend in enough ice water, 2 tablespoons at a time, to form moist clumps. Gather dough into a ball; cut in half. Flatten each half into a disk. Wrap separately in plastic wrap; refrigerate until firm, about 1 hour.

Filling
3 1/2 cups 1/2-inch thick slices trimmed
    rhubarb (1 1/2 pounds untrimmed)
3 1/2 cups strawberries, hulled and halved
1/2 cup packed golden brown sugar
1/2 cup sugar
1/4 cup cornstarch
1 teaspoon ground cinnamon
1/4 teaspoon salt
1 large egg yolk, beaten, to blend
    with 1 teaspoon water (for glaze)

Preheat oven to 400 degrees F. Combine first 7 ingredients in a large bowl; toss gently to blend.

Roll out 1 dough disk on a floured work surface to a 13-inch round. Transfer to a 9-inch diameter glass pie dish. Trim excess dough, leaving a 3/4-inch overhang.

Roll out second dough disk on a lightly floured surface to a 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.

Brush glaze over crust. Transfer pie to a baking sheet. Bake for 20 minutes. Reduce oven temperature to 350 degrees F. Bake pie until golden and filling thickens, about 1 hour 25 minutes.

Transfer pie to a cooling rack to cool completely.