Preheat oven to 350°. Line a 9x13 pan with tin foil, spray with nonstick spray. Set aside.
Combine the melted butter and brown sugar in a medium sized bowl.
Add in the eggs and vanilla. Mix well.
Add in the salt, baking powder, and flour. Mix until just combined.
Stir in any add-ins you'd like.
Pour the batter into the prepared 9x13 pan. Spread to cover the bottom of the pan.
Bake at 350° for 20-25 minutes or until barely golden brown. DO NOT OVER BAKE.
Remove from the oven, cool completely. Pull the blondies out of the pan using the aluminum foil once completely cool. Slice and serve.
