Chocolate Chip Marshmallow Cookies

Melt butter in a medium sauce pan on medium heat. Stir the butter to make sure it melts evenly. Once the butter is completely melted, it will start to foam up. Continue stirring the butter. As it cooks, it will start to change into a deeper color. This could take 6-8 minutes. You'll start to notice a nutty aroma and the butter will begin to have brown specs at the bottom of the pan. The entire process of browning butter from start to finish should not take more than 10 minutes on medium heat. Once butter is browned, pour it into a heat proof bowl and set it aside to cool for about 5 or 10 minutes.
½ cup (113.5 g) unsalted butter

Preheat the oven to 350℉ and line a large baking sheet with parchment paper.
In a small bowl, add the flour, baking soda, baking powder, salt, and espresso powder and whisk together, then set aside.
1½ cups (180 g) all purpose flour, ½ teaspoon salt, ½ teaspoon baking soda, ¼ teaspoon baking powder, ¼ teaspoon espresso powder
In a medium bowl, add the brown butter, brown sugar, and granulated sugar and mix using a spatula or whisk until combined.
½ cup (125 g) + 2 tablespoon brown sugar, packed, 3 tablespoon (37 g) granulated sugar
Add the whole egg, egg yolk, and vanilla extract and mix until completely combined. Then add the dry ingredients and mix until incorporated.
1 large whole egg + 1 egg yolk, 1 teaspoon vanilla extract
Add the chopped chocolate and mix using a spatula, then spoon the marshmallow fluff in various places in the batter and then fold it into the batter using a spatula. You'll notice streaks of marshmallow fluff in the batter.
3.5 oz. dark chocolate, chopped (I use 70%)
Using a 3 tablespoon cookie scoop, scoop cookie dough onto the baking sheet, making sure to have a couple inches between each cookie. If you want, you can add a little marshmallow fluff on top of each cookie.
2-3 tablespoon Marshmallow fluff
Bake the cookies for 9-11 minutes, depending on how crispy you like your edges.