Combine 2 cups almond flour, 1 1/4 cups arrowroot, 1/3 cup sugar, 1 teaspoon salt, 1 teaspoon xanthan gum, and 1/4 teaspoon baking powder in a medium bowl. Stir in 3/4 cup spectrum shortening until mixture resembles coarse meal. Stir in 1/3 cup water and stir to make a dough.
Sprinkle a large piece of parchment paper with additional arrowroot starch. Roll dough out to about a 17- x 12-inch rectangle.
Carefully transfer dough evenly into a 15 1/2- x 10 1/2-inch jellyroll pan coated with cooking spray. Press together any breaks or cracks in dough. Chill.
Stir together remaining crust ingredients and roll out to another 17- x 12-inch rectangle on parchment sprinkled with arrowroot starch. Cut out leaves or small shape to allow pie to vent while cooking.