9 steps, about 22 minutes start to finish.
Preheat oven to 350°F. Grease a 6-inch cast iron skillet or small oven-safe baking dish.
In a medium bowl, whisk together the melted butter, granulated sugar, and brown sugar until combined.
Add the egg yolk and vanilla extract; whisk until smooth.
Stir in the flour, baking powder, and salt until just combined. Do not overmix.
Fold in the chocolate chips.
Drop spoonfuls of peanut butter across the dough and swirl gently with a knife or toothpick.
Press the dough evenly into the prepared skillet.
Bake for 11–14 minutes until the edges are set and golden but the center is still slightly underdone.
Remove from oven and let cool for 2–3 minutes. Serve warm directly from the skillet, ideally topped with vanilla ice cream.
“The center should look slightly underbaked when you pull it from the oven. It will continue cooking from residual heat. Don't overbake!”
