Using frozen marshmallows keeps them gooey and molten inside instead of burning. When you break a fresh cookie in half, the marshmallow stretches in this incredibly satisfying way that looks amazing and tastes even better. The cookies are thick, soft, and chewy with crispy edges, and that warm marshmallow center tastes exactly like a s'more.
Preheat your oven to 350°F (175°C) and line a baking sheet with parchment paper.
Cream together the unsalted butter, brown sugar, and granulated sugar in a large bowl until light and fluffy (about 2 minutes).
Beat in the egg and vanilla extract until fully incorporated.
Mix in the flour, baking soda, and salt until just combined. Stir in the semi-sweet chocolate chips.
Scoop out a heaping tablespoon of dough, flatten it in your hand, and wrap it around one frozen marshmallow, sealing the edges completely.
Place each dough ball on the baking sheet, spacing at least 2 inches apart.
Bake for 11-13 minutes, until edges are golden but centers are slightly underdone for that gooey marshmallow effect.
Cool for 5-10 minutes before pulling apart—watch for the marshmallow stretch!