Preheat your oven to 350°F (175°C). This step is essential to ensure your White Chocolate Pecan Blondies bake evenly.
Line your 9x13 inch baking pan with parchment paper, leaving some overhang on the sides to make it easier to lift the blondies out later. Grease the parchment lightly to prevent sticking.
In a mixing bowl, whisk together the all-purpose flour, baking powder, and kosher salt to evenly distribute the leavening agent.
In a separate bowl, combine the melted butter and light brown sugar. Whisk until well combined. Add in the eggs and vanilla extract, whisking until the mixture is smooth and shiny.
Gradually add the dry ingredient mixture into the wet ingredients, stirring gently with a spatula until just combined. It’s okay if there are a few lumps.
Gently fold in the white chocolate chips and chopped pecans, distributing them evenly throughout the batter.
Pour the batter into the prepared baking pan, spreading it out evenly. Bake for 20-25 minutes, or until the edges are lightly golden and a toothpick inserted into the center comes out with a few moist crumbs.
Remove the blondies from the oven and let them cool in the pan for about 10 minutes. Then lift them out using the parchment overhang and cool completely on a wire rack. Sprinkle with flaky sea salt if desired before cutting.