Grandma's Strawberry Rhubarb Pie

Ingredients

• 2 cups all-purpose flour, plus more as needed
• 1/2 cup cake flour
• 3 teaspoons powdered sugar, sifted
• 1/2 cup shortening, butter-flavored
• 1/4 cup butter, salted
• salt, to taste
• 1 egg
• 2 teaspoons vinegar
• 1/4 cup water, ice cold
• 2 1/2 cups red rhubarb, chopped
• 2 1/2 cups strawberries, de-stemmed, washed, and cut
• 1 1/2 cups sugar
• 2 tablespoons minute tapioca
• 1 tablespoon all-purpose flour
• 1/2 teaspoon lemon juice
• 1/2 teaspoon lemon zest
• 1/2 teaspoon ground cinnamon
• 1 teaspoon vanilla extract
• 3 tablespoons butter, cut into small cubes
• 1 egg white, beaten with 1 teaspoon water
• large granule sugar, optional, to taste, for garnish