Preheat the oven to 350 degrees.
Combine butter, peanut butter, sugar, and brown sugar in a large bowl and mix together till creamy.
Stir in the vanilla and the egg and mix till just combined.
Add salt, baking soda, flour and mix. (Start with 1 1/4 cup flour and add more in one tablespoon at a time until the cookie dough is a good texture, not to sticky, and not too dry)
Roll cookies into 1 tablespoon sized balls. Place into remaining sugar and roll to coat.
Place balls on a cookie sheet lined with parchment or silicone, about 2 inches apart from each other.
Bake for 8-9 minutes until the cookies are golden and just start to crack.
Remove cookies from the oven and push a chocolate kiss into the top of each cookie (they will crack more).
Allow cookies to set on pan for another 3-4 minutes, then carefully move to a cooling rack and allow to cool completely.