Preheat your oven to 350°F (175°C). Line your 9x13-inch baking pan with parchment paper, leaving some overhang for easy removal later.
In a medium saucepan, melt the unsalted butter over low heat. Once melted, remove it from the heat and let it cool slightly.
In a large mixing bowl, whisk together the melted butter, granulated sugar, and packed light brown sugar until well combined. Add the eggs one at a time, mixing well after each addition. Stir in the vanilla extract.
In a separate bowl, whisk together the all-purpose flour, baking powder, and kosher salt.
Gradually add the dry mixture into the wet mixture, using a spatula to fold until just combined. Be careful not to overmix.
Fold in the chopped chocolate until evenly distributed throughout the batter.
Pour the batter into the prepared baking pan, spreading it evenly. Bake for 25-30 minutes, or until the edges are golden brown and a toothpick inserted in the center comes out with a few moist crumbs.
Allow the blondies to cool in the pan for about 10 minutes before lifting them out using the parchment paper. Let them cool completely on a wire rack before slicing into squares.
