In a stand mixer fitted with the paddle attachment, or in a large bowl with a hand mixer, beat the butter with the sugar and light brown sugar for 2 minutes. It should be light, fluffy, and have turned a slightly paler color.
½ cup unsalted butter, ½ cup white sugar, ½ cup light brown sugar
Stop the mixer and use a rubber spatula to scrape the sides and bottom of the bowl. Add the egg and vanilla extract, then beat again on medium speed for 1 minute until combined.
1 large egg, 1 teaspoon vanilla extract
Stop the mixer and add all of your dry ingredients - flour, baking powder, baking soda, salt and cocoa powder. Beat on low speed so the dry ingredients don't go flying out! Make sure to stop the mixer and scrape the sides and bottom of the bowl again so everything gets mixed together.
1 teaspoon kosher salt, 1 ¾ cups all purpose flour, ½ teaspoon baking powder, 1 teaspoon baking soda, ⅓ cup dutch processed cocoa powder
Place in the fridge for 45-60 minutes - note this is a sticky dough so the chilling will help with scooping!
Preheat the oven to 350°Fahrenheit/175°Celsius and line 2 baking sheets with parchment paper. Take the marshmallows out of the freezer.
Scoop out 2 heaping tablespoons of dough cookie and use your palm to flatten the dough. Place a marshmallow in the middle, and then cover the marshmallow completely in the dough. You don't want any marshmallow peeking out or it will melt! Roll the cookie dough ball in the extra white sugar.
extra sugar for rolling
Place the cookie dough balls on the parchment lined baking sheet. Make sure to leave about 2 inches of space between each cookie, I usually do 5 cookie dough balls to 1 baking sheet. While one sheet is baking, I place the other sheet in the fridge or freezer.
Bake the cookies for 8-10 minutes.
Notes
My recipes have been developed and tested in metric grams. I highly recommend using a weighing scale and measuring out your ingredients the metric way. .Salt: If you don’t have kosher salt, halve the amount of salt called for in the recipe. 1 teaspoon kosher salt = ½ teaspoon fine salt. I'm using Diamond Crystal Kosher Salt and not Morton Salt, which is too salty. Chocolate Chips: to make these cookies extra chocolatey, gently press on chocolate chips as soon as they come out of the oven.Marshmallows Melting: freezing the marshmallows beforehand is going to help them not melt. Also make sure the marshmallows are completely covered in cookie dough, or they will seep out and melt. Storage: keep the baked cookies in a tupperware for up to 1 week at room temperature. Freeze unbaked cookie dough balls for up to 3 months. When ready to bake, take them out of the freezer and bake at the same temperature as above but for an extra minute or two.