Preheat oven to 350 degrees F. Line a 12-cup muffin pan with paper liners. Set aside.

Whisk together the flour, baking powder, and salt in a medium bowl and set aside. Using a mixer, cream together the peanut butter, butter, and brown sugar until light and fluffy (about 2 minutes on medium speed). Beat in the eggs one at a time, followed by the vanilla. Scrape down the sides as needed.

Slowly beat in the flour mixture alternately with the buttermilk, starting and ending with the flour mixture. Stir until just combined. Do not overmix. The batter will be thick. Divide batter evenly among the cupcake tins. Bake for 22-24 minutes or until a toothpick comes out clean. Cool completely.

To make the frosting, start by toasting the sesame seeds in a dry pan over medium heat until fragrant, about 5 minutes. Put them in a plastic zip top bag with the air pressed out of it. Using a rolling pin, smash the sesame seeds until you get a rough powder.

Beat the butter at medium speed for 2 minutes, until fluffy. Gradually sift in the powdered sugar and beat. Beat in the black sesame powder, vanilla, and salt. Frost!