Using a wooden spoon, a spatula, or a handheld or stand mixer fitted with a paddle attachment (on medium speed), mix butter and peanut butter until combined and creamy. Add vanilla and salt and mix until combined. Add 2 cups powdered sugar and beat until combined. It’s ok if the mixture is a little crumbly or soft. Add more powdered sugar as needed until you can easily form the mixture into balls.
Roll peanut butter dough into 1.5-inch/4 cm (or any size you want) balls and place on a baking sheet lined with parchment paper. Place in the refrigerator for 1 hour or until firm.
Peanut butter balls can be kept in an airtight container in the refrigerator for 5 days.