1. Preheat the oven to 350°F, with a rack in the center position. Grease a 12-cup muffin tin with cooking spray or butter.
2. In a large bowl, cream together the butter and brown sugar until light and fluffy. Beat in the vanilla and egg.
3. In a smaller bowl, stir together the flour, graham cracker crumbs, and baking powder. Add the dry ingredients to the butter-sugar mixture and mix gently until just combined.
4. Measure out 1/2 cup of the dough and set aside for the topping. Press the remainder evenly into the prepared muffin cups, filling each about one-fourth full.
5. Spoon 1 tablespoon of the marshmallow crème over each cup, then top with a sprinkle of chocolate chips, dividing them evenly among the cups. Crumble the reserved dough over the chocolate chips, and top each cup with a pinch of sea salt.
6. Transfer to the oven and bake until the marshmallow crème is puffed and the dough is deeply golden brown, about 15 minutes.
7. Allow the cups to cool slightly before running a paring knife around the edges of each one to pop out of the pan. Serve warm or at room temperature.

Source: Reprinted from One Pan & Done. Copyright © 2017 by Molly Gilbert. Photographs copyright © 2017 by Aran Goyoaga. Published by Clarkson Potter/Publishers, an imprint of Penguin Random House, LLC.