Ingredients
Equipment
Method
Make the dough
- Heat the oven to 350°F and line two 18x13-inch rimmed baking sheets with parchment paper.
- Beat the softened butter, granulated sugar, and packed light brown sugar in a large bowl with an electric mixer on medium speed until fluffy, about 2 minutes.
- Beat in the egg and vanilla extract until smooth.
- Whisk the all-purpose flour, unsweetened cocoa powder, baking soda, and salt in a medium bowl.
- Add the flour mixture to the butter mixture and mix on low just until combined.
- Stir in the semisweet chocolate chips.
- Scoop the dough into 24 rounded tablespoon-size portions.
- Arrange 12 portions on each baking sheet, spacing them about 2 inches apart.
Bake and top the cookies
- Bake one sheet at a time for 8 minutes, until the edges are set and the centers still look soft; top that batch before baking the next sheet.
- Remove the sheet from the oven and press a marshmallow half, cut side down, onto each cookie.
- Return the sheet to the oven for 2 to 3 minutes, until the marshmallows puff and soften, then repeat with the second sheet.
- Cool the cookies on the baking sheets for 5 minutes.
- Transfer the cookies to a wire rack to cool.
Notes
For the softest centers, remove the cookies when the edges are set and the centers still look soft. Store airtight at room temperature for up to 4 days; freeze for up to 2 months. For a dairy-free swap, use dairy-free butter and semisweet chocolate chips.