1/2cup(4 ounces; one stick) unsalted butter, melted
1/2cupcreamy peanut butter
1and 3/4 cups dark brown sugar, packed
2large eggs, at room temperature
1/2teaspoonsalt (fine sea salt, table salt, or kosher salt will all work)
1 1/2cupswhite chocolate chips
1cuppeanut butter chips
1teaspoonflaky sea salt (I used Maldon Sea Salt and think it's the best), for sprinkling, optional
Preheat oven to 350 degrees (F). Line a 9" x 13" pan with parchment paper; lightly grease the paper and set aside.
Melt the butter in a medium saucepan over medium-heat. Remove from heat and stir in the peanut butter and brown sugar, whisk well to combine.
Whisk in eggs, one at a time, beating well after each addition. Stir in the salt, flour, and baking powder, mixing just until combined. Fold in the white chocolate chips and peanut butter chips.
Spread the mixture evenly in the pan, then sprinkle the top with additional white chocolate chips and peanut butter chips, if desired. Bake the blondies for 15 minutes, then cover the pan with aluminum foil and bake for another 15-18 minutes, or until they're light brown on the edges and top. Carefully remove them from the oven and cool completely before cutting.