Preheat the oven to 350 degrees.
Combine butter, peanut butter, sugar, and brown sugar in a large mixing bowl. Cream together for about 2 minutes till creamy.
Stir in the vanilla and egg and mix till just combined.
Add in the salt, baking soda, flour and mix till smooth.
Roll cookies into a heaping tablespoon sized balls.
Roll into remaining sugar to coat.
Place balls onto a cookie sheet lined with silicone or parchment.
Bake for 9-10 minutes until the cookies are golden and start to crack.
Remove cookies from oven and push top in using the bottom of a small spice container (or any circular thing with a flat bottom that is about 2 inches across)
Allow to cool on pan for about 2 minutes, then move to cooling sheet to cool completely.