01 -
Fire up your oven to 350°F. Coat a 9x13-inch pan with some non-stick spray, or lay in parchment paper if you want a hassle-free way to lift the bars out.
02 -
Combine the melted butter with the crushed graham crackers in a mixing bowl. Stir until it all sticks together, then press it evenly into the pan to make the base.
03 -
Drizzle the sweetened condensed milk over the top of the crust. Spread it around so the entire surface is coated.
04 -
Scatter 1 cup of marshmallows, all the chocolate chips, and the graham cracker chunks evenly over the sweet, milky surface.
05 -
Slide the pan into the oven and bake for 15 minutes. The edges should start bubbling and the marshmallows turning puffed and golden.
06 -
Pull the pan out of the oven and scatter the rest of the marshmallows on top, making sure to cover any open spots.
07 -
Bake for another 10-15 minutes until the marshmallows on top are golden and just toasted, and the edges of the bars are stable.
08 -
Once out of the oven, drop the chocolate bar pieces onto the marshmallows while they’re still hot enough to melt a little.
09 -
Cool on a wire rack for at least 15 minutes before slicing. If you want clean cuts, you’ll want to let them cool completely—they’ll still be soft and gooey.