Preheat and prep: Set your oven to 350°F (175°C). Line two baking sheets with parchment paper for easy cleanup and even baking.

Cream the fats and sugars: In a large bowl, beat softened butter, peanut butter, granulated sugar, and brown sugar until light and smooth, about 1–2 minutes. This step helps your cookies bake up soft and fluffy.

Add egg and vanilla: Mix in the egg and vanilla extract until fully combined and glossy. Scrape the bowl to catch any streaks of peanut butter.

Whisk dry ingredients: In a separate bowl, whisk together flour, baking soda, and salt. This keeps the leavening evenly distributed.

Combine wet and dry: Add the dry mixture to the wet ingredients. Mix on low just until no dry flour remains. Do not overmix or the cookies can get tough.

Melt the chocolate: In a microwave-safe bowl, heat the chocolate chips in 20–30 second bursts, stirring between each, until smooth. Let it cool for 2–3 minutes so it’s warm but not hot.

Create the swirl: Dollop the melted chocolate over the cookie dough in 4–5 spoonfuls. Using a butter knife or spatula, gently fold the chocolate through the dough 2–3 times. Stop while you still see ribbons and streaks; if you mix too much, the dough will just turn brown.

Portion the dough: Scoop 2-tablespoon mounds (a medium cookie scoop works great) and place them 2 inches apart on the baking sheets.

Bake: Bake for 9–11 minutes, until the edges look set and the centers still look a touch soft. They’ll finish setting as they cool.

Finish and cool: If you like, sprinkle a pinch of flaky sea salt on top right after baking. Let cookies cool on the sheet for 5 minutes, then transfer to a rack to finish cooling.