Preheat oven to 350°F (175°C). Line an 8×8-inch baking pan with parchment paper.

Cream butter and both sugars until light and fluffy. Beat in egg and vanilla.

In a separate bowl, whisk flour, graham crumbs, baking powder, and salt.

Gradually add dry mix to wet ingredients until a dough forms.

Press two-thirds of the dough into the pan. Sprinkle chocolate chips and marshmallows evenly.

Crumble and drop remaining dough on top, gently pressing down.

Bake 20–25 minutes, until golden brown and marshmallows are slightly toasted.

Cool completely before slicing (this helps everything set nicely).