Design Eat Repeat

1 Preheat oven to 350℉.
2 In a large microwave-safe bowl, melt the unsalted butter [adjustable](½ cup, i.e. 1 stick)[/adjustable] for 45-60 seconds until melted. I recommend covering your bowl with a paper towel to prevent splattering.
3 Add light brown sugar [adjustable](½ cup) and granulated sugar (½ cup)[/adjustable] and mix until combined. 
9 Mix in eggs [adjustable](1 whole egg + 1 extra yolk) and vanilla extract (2 teaspoons)[/adjustable]. Stir in creamy peanut butter (½ cup).
4 Mix in baking soda [adjustable](½ teaspoon), baking powder (½ teaspoon), and salt (½ teaspoon)[/adjustable].
10 Add all-purpose flour [adjustable](1 ¼ cups)[/adjustable] and mix until all the flour disappears into the dough.
5 Let dough sit for 5 minutes to firm up a little. If dough still seems too sticky to form, place in the refrigerator for 5-10 minutes.
6 Line a baking sheet with parchment paper. Scoop dough into 4-tablespoon-sized scoops.
11 Roll dough into balls and then create a larger crater in the middle. Scoop or pipe 1 tablespoon of marshmallow fluff and cover with the dough. Roll into a smooth ball.
7 Bake at 350℉ for 10-11 minutes, or until edges are lightly golden brown. For soft & chewy cookies, it's best to take them out before the edges are brown. They will continue to firm up as they cool.
8 Remove from oven and place entire pan on a cooling rack. Top with flaky sea salt, if desired.
12 Allow the cookies to cool on the hot pan for 15-20 minutes before removing them. This will allow them to finish baking on the hot pan. For the best texture, wait 1-2 hours to eat.Once cooled, use a spatula to transfer them to a wire cooling rack.