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Preheat oven to 350 degrees F. Line and grease a 9x9-inch baking pan with parchment paper.
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Add the melted butter and brown sugar to the bowl of an electric stand mixer, fitted with the paddle attachment. Beat until smooth and creamy.
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Scrape down the sides, with the mixer on low, add in one egg at a time. Scrape down the sides as needed. Add in vanilla. Mix on medium until well combined.
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Add the flour, baking powder, cinnamon, salt, and baking soda to the bowl. Mix on low to combine. Mix until no more flour is visible.
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Transfer batter to prepared dish. Smooth out into one even layer.
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Mix the sugar and cinnamon for the topping together in a small bowl. Dust the entire top of the blondies with the cinnamon sugar.
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Bake for 30-35 minutes until a toothpick inserted into the center comes out clean. Let the blondies cool for at least 2 hours before slicing. The blondies will rise and sink as they cook and cool.