Preheat your oven to 350°F (175°C). Grease and line a 9x13 inch baking dish with parchment paper, allowing some overhang for easy removal.
In a medium saucepan, melt the butter over medium heat, stirring frequently. Continue cooking while whisking until the butter turns a deep golden brown and smells nutty, about 5-7 minutes. Remove from heat and let cool slightly.
In a large mixing bowl, combine the brown butter, brown sugar, and granulated sugar. Whisk until well combined and smooth.
Add the eggs one at a time, beating well after each addition, then stir in the vanilla extract.
In a separate bowl, whisk together the flour, baking powder, baking soda, cream of tartar, salt, and 1 teaspoon of cinnamon.
Gradually mix the dry ingredients into the wet ingredients until just combined. Be careful not to overmix.
Spread the batter evenly into the prepared baking dish, smoothing the top with a spatula.
In a small bowl, mix together the remaining 1/4 cup granulated sugar and 1 teaspoon cinnamon. Sprinkle this mixture evenly over the top of the blondie batter.
Bake in the preheated oven for 20-25 minutes or until the edges are golden and a toothpick inserted into the center comes out clean or with a few moist crumbs.
Remove from the oven and allow to cool in the pan for about 10 minutes. Then lift out using the parchment overhang and let cool completely on a wire rack.
Once cool, cut into squares and serve.
Notes
Allow to cool completely before cutting for best results.
Keyword blondies, brown butter, dessert, snickerdoodle