01 -
Preheat the oven to 350°F (175°C). Line an 8 by 8-inch metal pan with foil or parchment paper and spray with non-stick cooking spray.
02 -
In a large microwave-safe bowl, heat the butter in 30-second increments until melted. Add the sugar to the hot butter and whisk to combine. Let cool until just warm.
03 -
Add the egg, egg yolk, and vanilla extract to the cooled butter-sugar mixture and whisk vigorously until smooth. Stir in the salt, baking powder, and flour using a rubber spatula. Gently fold in 170 grams of the mix-ins.
04 -
Pour the batter into the prepared pan and top evenly with the remaining 85 grams of mix-ins.
05 -
For a soft center, bake for 25 to 28 minutes until the edges are lightly golden but the center still jiggles. For a firmer texture, bake for 30 to 35 minutes until the edges are golden brown and the center is set. Cool the blondies on a wire rack before cutting.
06 -
Sprinkle with flaky sea salt before serving. Allow the blondies to cool completely for optimal texture.