Pre-heat your oven to 350° F, and line a couple of baking sheets with parchment paper.
In a medium sized bowl, whisk together the flour, baking powder and salt.
In a large bowl, or in the bowl of a stand mixer, combine the melted butter, peanut butter, brown sugar, granulated sugar, egg and vanilla. Beat on medium-high speed until smooth.
Add the flour mixture to the peanut butter mixture, and mix until just combined.
Scoop out a heaping tablespoon sized mound of dough and roll it into a ball. Roll the ball in the 1/4 cup of granulated sugar until coated.
Place the dough balls onto the parchment lined baking sheet about 2 inches apart.
Use a fork to create crosshatch lines on the top of each cookie.
Bake for 12-14 minutes until the edges of the cookies start to turn golden brown.
Allow cookies to cool on tray for a few minutes before transferring them to a wire cooling rack.