Ingredients:

• 1 frozen pie crust (see pie crust recipe for instructions to make your own)
• 3 1/2 to 4 cups chopped rhubarb stalks (about 1 pound)
• 3/4 cup white granulated sugar
• 1 tablespoon orange zest
• 1/4 teaspoon cinnamon
• 1/4 teaspoon ground ginger
• 3 tablespoons instant tapioca or 2 tablespoons tapioca flour/starch (can sub 2 tablespoons corn starch)
• 1 tablespoon cornstarch
• 1/3 cup cold water
• 1/4 teaspoon cream of tartar (can use vinegar instead of cream of tartar, see method instructions)
• 1/2 cup white granulated sugar
• 4 large egg whites (room temperature)
• 1/2 teaspoon vanilla extract