Preheat your oven to 350°F (175°C) and line a baking sheet with parchment paper or a silicone mat to keep your cookies from sticking.
Beat the salted butter and peanut butter until the mixture is smooth and airy. Add the dark brown sugar and granulated sugar, mixing until glossy and combined.
Crack the egg and pour in the vanilla. Stir everything together until the dough comes together, soft and a little sticky.
Sprinkle the flour and baking soda over the dough, then gently fold it in with a spatula or wooden spoon. Be careful not to overmix, just enough to combine and keep the cookies tender.
Fold in most of the dark chocolate chips, saving a few to press on top of each dough ball for that perfect chocolatey finish.
Use a scoop or your hands to form dough balls. Place them 4 inches apart on your baking sheet so they bake into nice, round cookies.
Bake for about 10 minutes until the edges are golden and firm, but the centers still look soft. Let the cookies cool on the baking sheet for 10 minutes, then transfer to a wire rack to cool completely, or enjoy warm if you can’t wait!