Snickerdoodle Crumb Bars
Streusel: Whisk together flour, brown sugar, and salt. Using your hands or a pastry cutter, cut in butter until small to medium clumps form. Refrigerate until ready to use.Advertisement
Topping: Stir together cinnamon and granulated sugar; set aside.
Bars: Preheat oven to 350 degrees. Butter an 8-inch square baking dish and line with parchment, leaving a 2-inch overhang on two sides. Butter parchment. Whisk together flour, baking soda, cream of tartar, and salt.
In a separate bowl, whisk together butter, both sugars, and eggs. Add flour mixture; stir to combine. Spread half of batter into bottom of dish. Sprinkle with half of cinnamon sugar. Dollop remaining batter on top; spread evenly with an offset spatula or the back of a spoon. Sprinkle evenly with streusel, then remaining cinnamon sugar. Bake until a tester inserted in middle comes out clean, 30 to 35 minutes. Let cool completely. Transfer to a cutting board using parchment overhang and cut into bars to serve, or store in an airtight container at room temperature up to 3 days.
To keep the layers intact, let the cake cool completely before cutting it into bars.