1/4 Cup Cornstarch
Directions: Line a casserole or 9x13 pan with foil the hangs over the sides. You will grab the ends to remove the bars after they have cooked. Spray with cooking spray or grease with softened butter.
Combine flour, sugar, and salt in a food processor or by hand with a fork. Slowly add the butter until it is well incorporated, creating a sandy consistency. Pour into the prepared pan and make an even layer. Refrigerate for 30 minutes.
Preheat the oven to 350. Place the pan in the oven and bake for 20 - 25 minutes or until lightly golden. Remove from oven.
While the bars are baking, make the filling.
Combine the eggs, sugar, and flour. Then, whisk in the sumac-ade, cured sumac, milk, and salt.
Reduce to oven temperature to 325. Give the filling a good stir and pour into the pan. Bake for about 20 minutes or until the middle of the bars stop wobbling. Remove from oven and let cool for at least 30 minutes. Carefully and quickly, pull on the foil tabs to lift the bars out of the pan and onto a cutting board. Cut the bars into squares.
**You will notice that the lovely color of the sumac-ade is lost in the baking process. We decided to use beet root to bring back that lovely red color. You can either add beet root to the filling so that the color seeps throughout. We preferred combing the beet root with confectioner's sugar and dusting over the bars before serving.
We adapted Cook's Illustrated's recipe for Lemon Bars from their Baking Book for a twist on a classic dessert. Tart and sweet, creamy with a shortbread crunch, these sumac bars are the perfect retreat for any time of the year.