Preheat oven to 350 degrees F
Combine peanut butter, brown sugar, egg, baking soda, chocolate chips, and vanilla in a mixing bowl until the sugar is fully incorporated and the mixture is no longer gritty.
Roll mixture into 2 inch balls. Place on ungreased cookie sheet spaced at least 2 inches apart, and bake for 8 to 10 minutes. (Don't worry if they look a little under baked, they firm up as they cool.)
Cool for 5-10 minutes then place on wire rack. These cookies are best when they are still soft and gooey!