Grinch Sugar Cookie Bars

Name: Grinch Sugar Cookie Bars
Prep time: 15 min
Cook time: 28 min
Total time: 43 min
Cuisine: American
Ingredients: 4 ¼ cup all-purpose flour; 1 tablespoon cornstarch; 1 teaspoon baking powder; ¼ teaspoon fine sea salt; 1 cup unsalted butter (softened); 1 ½ cups granulated sugar; 3 large eggs; 2 teaspoons vanilla extract; ½ cup green jimmie sprinkles; ½ cup unsalted butter (softened); 2 ½ cups powdered sugar; pinch of fine sea salt; 1 ½ teaspoons vanilla extract; 1 ½ tablespoons whole milk; green gel food coloring; yellow gel food coloring; red gel food coloring