In a mixing bowl, combine the mascarpone cheese, 2 tablespoons of heavy cream, vanilla extract, powdered sweetener, and peanut butter. Use a hand mixer to blend everything until it's wonderfully smooth and creamy.
Using a cookie scoop (or just a spoon), form the mixture into small, even balls and arrange them on a sheet pan lined with parchment paper.
Pop the sheet pan into the freezer for about 10 minutes, just until the truffle balls are firm enough to handle easily.
For the chocolate coating, place the sugar-free chocolate chips and the remaining 1 tablespoon of heavy cream in a microwave-safe bowl. Microwave for 30 seconds, then stir. Continue microwaving in 10-second bursts, stirring well after each, until the chocolate is fully melted and beautifully smooth. (You can also melt the chocolate over a double boiler if you prefer).
Carefully spoon the melted chocolate over each chilled truffle, ensuring it's fully coated, then return them to the parchment paper. Place them back in the freezer for another 10 minutes to set the chocolate shell.
Serve these delightful truffles as they are, or for an extra special touch, drizzle a little runny peanut butter on top and chill in the fridge until firm before enjoying!