Preheat the oven to 350° F. Line a large cookie sheet with parchment paper or a silicone baking mat.

Melt and cool the butter for a few minutes. Combine the melted butter with the brown and granulated sugar. Beat on medium speed until well combined. Next, add the egg and vanilla extract and continue beating until well incorporated.

Combine the dry ingredients in a separate bowl, stir to combine and add the dry ingredients into the dough, mixing on low speed until the dough starts to form. Before the dough thickens, add the chocolate chips and finish mixing with a spatula.

Scoop the dough using a medium-sized cookie scoop and place on a baking sheet, 2 inches apart. Bake for 7-8 minutes. Quickly remove from the oven and place a large marshmallow into the center of each cookie. Return to the oven and bake for another 3 minutes (total bake time 10-12 minutes).

Remove from the oven and gently push down the marshmallow in the center. Allow to cool on the baking sheet for 15 minutes before transferring to a wire rack to cool.

Finely chop the chocolate bar into small pieces, place in a microwave-safe bowl and microwave for 30 seconds, stir. Microwave for 20 seconds, but at 50% power and stir until the remaining chocolate is melted. If needed, add an additional 10-15 seconds in the microwave at 50% power until the chocolate is melted and smooth.

Using a spoon, place a dollop of chocolate over the marshmallow and use the back of