01 -
Turn your oven on to preheat at 350°F (175°C). Line an 8×8-inch metal pan with foil or parchment paper, leaving some overhanging the edges, and give it a light coat of nonstick spray.
02 -
Put the butter in a big microwave-safe bowl and heat it until it melts. Mix in the brown sugar and peanut butter until smooth, then let it cool down a little.
03 -
In another bowl, whisk together the flour, crushed graham crackers, baking powder, baking soda, and salt. Set this mixture aside for later.
04 -
Once the butter mixture is barely warm, stir in the egg and egg yolk, one after the other, whisking each in fully. Add the vanilla extract, then gently fold in the dry ingredients until the batter just comes together. The dough should feel thick.
05 -
Take about two-thirds of your blondie dough and press it firmly into the bottom of the prepped pan. Aim for an even surface.
06 -
Spoon and spread the marshmallow creme over the base layer—you don’t have to make it perfect. Scatter chocolate chips evenly on top of the marshmallow layer.
07 -
Grab little chunks of the leftover dough, flatten them between your hands, and lay these pieces on top of the chocolate and marshmallow layers. Aim to cover about two-thirds of the surface.
08 -
Slide the pan into the oven and bake for 26–28 minutes. The middle should wiggle just a little, while the edges are set and golden. Watch for the marshmallow to puff up and brown slightly. Don’t let it overcook, or the blondies might end up dry.
09 -
Leave the blondies to cool completely in the pan. Once cooled, lift them out using the parchment or foil overhang. Slice into squares and enjoy.