Begin by preheating the oven to 350 degrees F. While the oven is preheating, place the butter in a microwave safe bowl and melt in the microwave for 60 seconds or until completely melted.
Place the melted butter, white granulated sugar, brown sugar in a large bowl and use a hand or stand mixer to beat on low for several minutes until very well combined.
Next, add the eggs, milk and vanilla extract and stir until the eggs are just combined. Add the flour, baking powder, cream of tartar, and salt to the large bowl and stir until just combined. Try no to over-stir.
Place the batter in a prepped 11x7 inch baking dish and smooth until it is in an even layer. The brownie batter will be thick so try your best.
In a separate small bowl add the remaining white sugar and cinnamon and stir to combine. Sprinkle over the top of the blondies in the backing dish.
Place the baking dish on the center rack and bake for 25-30 minutes or until a toothpick comes out clean. Once baked, serve the snickerdoodle blondies warm or store leftovers accordingly. Enjoy!
Leftover Storage: To store leftover snickerdoodle blondies either cover the cooled pan with foil or remove brownies in a airtight container at store at room temperature. When stored correctly the blondies will stay good for up to 1 week.
Freezing Instructions: Slice the brownies into squares are wrap each one in parchment paper then in foil and place in a freezer bag for up to 3 months.
Fold in the Dry Ingredients: It is important to not over-stir the dry ingredients into the wet ones or the blondies will be more cake-like and less fudgey/chewy.
Baking Tip: When making these snickerdoodle brownies try your best not to over-bake the blondies. Bake them until a inserted toothpick comes out mostly clean with some moist crumbs but no wet batter.