Combine butter, peanut butter, powdered sweetener, and vanilla extract (if using) in a medium-sized bowl.
Using a cookie scoop, divide peanut butter mixture into 30 evenly sized balls about 1-inch in diameter. freezer for about 30 minutes to ensure they are firm.
Towards the end of the freezing time, start melting the chocolate in a double boiler or chocolate melter. I don't recommend using a microwave because it's easy to burn the chocolate if you aren't careful to do it in very small increments stirring after each.
Remove balls from freezer and dip most of the way into the chocolate leaving an uncovered circle at the top. Placing a toothpick into each frozen ball works well for dipping, but don't remove the toothpick until the chocolate is set. You may need to tip the pot to get a deep enough amount of chocolate. Once coated in chocolate, place in refrigerator to set.
