In a bowl over a pot of boiling water, melt the chocolate and butter until smooth.
Turn off burner and leave the bowl over the water to keep warm.
In the bowl of a stand mixer, beat the eggs, granulated sugar and brown sugar for 5 minutes.
Turn the mixer to the lowest setting and slowly pour in the chocolate butter.
Mix until just combined.
Fold in the flour, salt, baking powder and vanilla extract.
In a small bowl, microwave the marshmallow fluff for 10-20 seconds until warmed and thinned.
Add a few tablespoons of marshmallow fluff to the batter and gently swirl.
Use a cookie scoop to scoop three tablespoon dollops onto a parchment paper lined baking sheet leaving two inches of room between each cookie.
Continue adding marshmallow fluff as need to create generous streaks.
Bake at 350F for 11 minutes.
Use 60% cacao or higher bittersweet chocolate: Chocolate with a high cacao will give these cookies a rich, chocolaty flavor and result in a smoother melt. Because we're adding sugar, we don't need to worry about the chocolate being bitter.
Bringing cold eggs to room temperature quickly: If you need to bring your eggs to room temperature quickly for this recipe, fill a bowl with hot water from your tap and place the eggs in it for about 5 minutes.
Whip the eggs/sugar for the full 5 minutes: This is the step that gives the cookies their crinkled brownie appearance so be sure to whip for the full 5 minutes.
Scooping: Try to scoop the batter so that the marshmallow fluff is at the bottom of the scoop. This will ensure you get a nice visible swirl that will toast and that will keep it from sticking to the parchment which could potentially tear the cookie when it's moved.
Fold in the dry ingredients: Once you whip the eggs and sugar, you want to minimize the amount of work the batter experiences so the eggs don't deflate.
Storage: These cookies can be kept in an air tight container at room temperature for up to a week or frozen (I like to individually wrap mine in plastic wrap) for up to 6 months.
Serving Size:1 cookie
Keywords: hot chocolate cookies, chocolate marshmallow cookies, chocolate cookie recipe