Preheat your oven to 350 degrees and line two baking sheets with parchment paper. In a small bowl, stir together the flour, baking soda, and salt, and set aside. In a large bowl, beat together the butter, peanut butter, brown sugar, and 1/4 cup sugar until well combined. Beat in the egg and vanilla extract until just combined. Finally, beat in the dry ingredients slowly until everything is well combined and you have a soft dough.

Scoop the cookies into 2-tablespoonfuls and roll each cookie in the additional granulated sugar. Place on your prepared baking sheets about 2 inches apart. Using a fork, press down the cookies gently to make a cross-hatch pattern on top. Bake for 10-12 minutes, or until the cookies start to look crackly and are puffed. The cookies will settle and finish cooking after you remove from the oven, so don't over-bake these! Cool completely and enjoy!