In a separate bowl, use a hand mixer on low setting to cream together the butter and sugar until light and fluffy. Beat in the egg, milk, peanut butter, and vanilla extract until just well combined. Note: Use softened butter for an easy time of creaming.
Shape the dough into 1-inch balls. Mix the extra granulated sugar and ground cinnamon in a bowl. Roll each cookie dough ball in the cinnamon-sugar mixture to coat.
1 tablespoon ground cinnamon, 2 tablespoons sugar for rolling
Place the sugared dough balls on the lined baking sheets, leaving about a 2-inches between them for the cookies to spread.
Bake for 9-11 minutes, or until the edges are set but the centers remain soft.
Remove from oven and Cool on the baking sheet for about 5 minutes before transferring the cookies to wire racks to cool complete