01 -
Preheat the oven to 350°F (175°C). Line an 8-inch square baking pan with parchment paper, leaving overhang on two sides.
02 -
Beat the softened butter, 1/2 cup peanut butter, and brown sugar until smooth and creamy. Mix in the egg and vanilla until fully combined.
03 -
Stir in the flour, baking powder, and salt just until a thick dough forms. Do not overmix once the flour disappears.
04 -
Press about two-thirds of the dough evenly into the prepared pan. Lightly grease a spatula, spread the marshmallow creme over the dough, and drizzle the warmed peanut butter over the top.
05 -
Flatten small pieces of the remaining dough between your fingers and place them over the marshmallow layer, leaving some marshmallow visible.
06 -
Bake for 26-30 minutes, until the edges are golden and the center looks set but still soft. Avoid baking until the whole top is deeply browned.
07 -
Cool in the pan for at least 1 hour. Lift out with the parchment, then slice with a lightly greased sharp knife.