Preheat oven to 350?F. Line baking sheets with parchment paper and set aside.

Cream butter and brown sugar together until smooth. Beat in the egg, vanilla, and peanut butter until completely combined.

Pour in flour and baking soda and mix until just incorporated, without over-mixing.

Scoop out 1-2 tablespoons of dough and roll into balls. If rolling in sugar, do that now. Place about 1 inch apart on the prepared baking sheet (they don't spread much).

Optional: Before baking, use the tongs of your fork to press down in both directions, making a criss-cross pattern.

Bake cookies for 7-8 minutes. Allow to cool for 5 minutes on the baking sheet before transferring to a wire rack to finish cooling completely.