Start by placing your unsalted butter in a saucepan over medium heat. Allow it to melt and then continue to cook, stirring frequently until it turns golden brown.
In a mixing bowl, combine the warm brown butter with the packed light brown sugar. Whisk them together until well combined. Add in the large egg and continue whisking until smooth and glossy.
In a separate bowl, whisk together the flour, baking powder, and cinnamon until evenly mixed.
Gradually add the dry ingredients to the wet ingredients, using a spatula to gently fold them together until just combined.
Fold in the semi-sweet chocolate chips and toasted walnuts until evenly distributed throughout the batter.
Preheat your oven to 350°F (175°C). Line your 8x8 inch baking pan with parchment paper and spread the blondie batter evenly in the prepared pan.
Before baking, sprinkle the top of the batter with flaky sea salt for a sweet and salty balance.
Place the pan in the preheated oven and bake for about 20-25 minutes, or until the edges are set and the center looks slightly underbaked.
Allow the blondies to cool in the pan for about 10 minutes before lifting them out using the parchment overhang. Transfer to a wire rack to cool completely before slicing.
