Preheat the oven: Start by preheating your oven to 350°F (175°C). Line a 9x13 inch baking pan with parchment paper, leaving some overhang for easy removal later.
Cream the butter and sugars: In a large mixing bowl, cream together the softened butter, brown sugar, and granulated sugar using an electric mixer on medium speed until the mixture is light and fluffy (about 2-3 minutes).
Add eggs and vanilla: Beat in the eggs one at a time, making sure each one is fully incorporated before adding the next. Then, add the vanilla extract and mix until combined.
Combine dry ingredients: In a separate bowl, whisk together the flour, baking powder, baking soda, salt, and 1 teaspoon of ground cinnamon until well combined.
Mix wet and dry ingredients: Gradually add the dry ingredient mixture to the wet ingredients, mixing on low speed until just combined. Be careful not to overmix; it's okay if a few flour streaks remain.
Spread in the pan: Pour the batter into the prepared baking pan and spread it evenly with a spatula.
Prepare cinnamon-sugar topping: In a small bowl, combine the tablespoon of granulated sugar and the teaspoon of ground cinnamon. Sprinkle this mixture evenly over the top of the blondie batter.
Bake: Place the pan in the preheated oven and bake for 20-25 minutes, or until a toothpick inserted in the center comes out clean with a few moist crumbs (not wet batter).
Cool and cut: Once baked, remove the blondies from the oven and let them cool in the pan for about 10-15 minutes. Then use the parchment overhang to lift them out of the pan and cool them completely on a wire rack. Once cooled, cut into squares.
Serve: Enjoy these delicious Snickerdoodle Blondies as a sweet treat or dessert!