Add the oil, granulated sugar, and brown sugar. Whisk until combined.

Add the eggs, vanilla extract, and buttermilk. Whisk until the mixture is smooth, well combined, and slightly thickened.

Add the flour, baking powder, and salt to the bowl. Gently fold the dry ingredients into the wet ingredients using a spatula, mixing until there are a few dry streaks of flour left. Then fold in the chocolate chips until evenly distributed. Be careful not to overmix, as this can make the muffins dense.

Let the batter rest while you preheat the oven to 425°F. Line every other well of a standard 12-cup muffin tin with paper liners (this helps create taller muffin tops).

Fill each liner all the way to the top with batter. Spoon a small amount of peanut butter onto each muffin and use a toothpick or knife to gently swirl it into the top. Sprinkle additional chocolate chips over each muffin.

Bake at 425°F for 5 minutes. Without opening the oven door, reduce the temperature to 350°F and continue baking for 10-14 minutes, or until the tops are set and a toothpick inserted into the center comes out clean or with a few moist crumbs.

Allow the muffins to cool in the pan for 5 minutes, then transfer them to a wire rack to cool completely. Finish with a sprinkle of flaky salt before serving.