Preparation
In a large mixing bowl, combine the softened butter and natural peanut butter.
Using an electric hand mixer, beat on medium speed until the mixture is completely smooth and creamy.
Add the vanilla extract and vanilla whey protein powder to the bowl.
Mix on low speed until just combined.
Gradually add the powdered Xylitol, mixing on low speed until a thick, cohesive dough forms. The mixture should be firm enough to roll.
Scoop out portions of the dough and roll them between your palms to form 24 uniform, bite-sized balls.
Arrange the balls in a single layer on a baking sheet lined with parchment paper.
Drizzle the melted sugar-free chocolate over the top of each ball.
Transfer the baking sheet to the refrigerator and chill for at least 2 hours, or until firm.