Preheat oven to 350°. Line a 9x13 pan with parchment paper, spray with cooking spray, and set aside.
Make the brown butter: To make brown butter, you’ll need to heat a skillet or saucepan over medium heat. Add the butter and stir it until melted. Continue stirring the butter even as it begins to foam and pop. Brown butter can turn into burnt butter easily, so keep stirring! After about 5-8 minutes, the milk solids will separate and fall to the bottom of the pan. Remove the brown butter from the pan and let it cool in a separate container as it can still continue to cook on a hot pan.
Mix the wet ingredients: Add brown sugar to a mixing bowl, and pour cooled brown butter in. Whisk until the sugar is dissolved into the butter. Mix in the egg and vanilla until combined.
Mix with the dry ingredients: In a separate bowl, whisk together the flour, salt, and baking powder until combined. Combine the dry mixture with the wet mixture being careful not to overmix. Fold in the chocolate chips and toasted pecans.
Assemble and bake: Pour the blondie batter into the prepared baking pan, then sprinkle the top with additional toasted pecans and chocolate. Bake for 23-25 minutes or until the center is set and the edges golden brown. Cool in the pan, then remove from the pan and cut into squares.