I started by preheating my oven to 350°F (175°C). While it warmed up, I prepared a 9x13-inch pan with parchment paper. This little step saved me so much hassle when it came to lifting the blondies out later.
In a large bowl, I whisked together the melted butter, brown sugar, and granulated sugar until smooth and glossy. Then I added the eggs and vanilla extract, mixing until the batter turned creamy. The eggs gave the blondies structure, while the vanilla added that cozy flavor.
In another bowl, I whisked flour, baking powder, baking soda, and salt. I gently folded this into the wet mixture, being careful not to overmix. Overmixing makes blondies tough, and I wanted mine soft and chewy.
In a small bowl, I stirred together sugar and cinnamon. This simple topping transforms the blondies into something special, creating that iconic snickerdoodle crust on top.
I spread the batter evenly into the pan, smoothed the top with a spatula, and sprinkled the cinnamon-sugar mixture all over. Into the oven it went for about 27 minutes. I knew they were ready when a toothpick came out with just a few crumbs.
I let the blondies cool completely in the pan before slicing them into squares. This step is hard because they smell so good, but patience pays off! Once cooled, they cut cleanly and held their shape beautifully.