Add the butter to a mixing bowl, and use a hand mixer to beat it until fluffy.
⅓ cup salted butter
Add in the peanut butter and beat again until combined.
1 cup peanut butter
Now, add in the vanilla extract and powdered sugar (you can add the sugar gradually) and mix until fully incorporated.
1 teaspoon vanilla extract, 1 ½ cups powdered sugar
Now, put the dough in the fridge for 1-2 hours to firm up.
Scoop about 1 tablespoon of the dough and roll it between your hands, forming a ball; repeat with the remaining batter, then put in the fridge for 30 minutes or so, then serve.
Notes
I usually store them at room temperature for up to 3 days and in the fridge for a whole week or so.