Snickerdoodle Bars

Name: Snickerdoodle Bars
Ingredients: 2 3/4 cups ( 352 g ) all-purpose flour , spooned and leveled; 2 teaspoons cream of tartar , sifted; 1 1/4 teaspoons fine sea salt; 1 teaspoon baking soda; 1 teaspoon ground cinnamon (Shauna Sever recommends Vietnamese cinnamon); 1 cup ( 225 g ) unsalted butter , at room temperature; 3/4 cup ( 170 g ) light brown sugar; 3/4 cup ( 150 g ) granulated sugar; 1 1/2 teaspoons vanilla extract; 2 large eggs , at room temperature; 1/4 cup ( 57 g ) whole milk; 3/4 cup ( 170 g ) unsalted butter , at room temperature; 1 1/2 cups ( 180 g ) powdered sugar; 1 teaspoon ground cinnamon , plus more for dusting (optional); 1 1/3 tablespoons whole milk; 1 teaspoon pure vanilla extract; 1/4 teaspoon fine sea salt