Preheat the oven to 350 F. Place powdered sugar into a shallow dish. In a medium bowl, whisk together flour, salt, and baking soda. In a large bowl, mic butter with peanut butter and sugar until smooth.
Add in the egg and vanilla extract, mix until smooth. Add in the flour mixture, and mix until a thick dough forms.
Roll the cookie dough into balls, and roll into the powdered sugar. Place onto a large ungreased baking sheet 2-inches apart. Bake for 10-12 minutes.