Place the cold mascarpone or cream cheese, powdered sweetener, smooth peanut butter, and vanilla extract in a mixing bowl. If your peanut butter is unsalted, add a pinch of sea salt.

Using an electric mixer, beat the mixture on medium speed until smooth and fully combined, scraping down the sides of the bowl as needed.

In a separate clean bowl, pour the cold heavy cream and whip with the electric mixer until soft peaks form (just below stiff peaks).

Fold about one-third of the whipped cream into the peanut butter mixture to lighten it, then gently fold in the remaining whipped cream until the mixture is uniform and no white streaks remain. Do not overmix.

Spoon or pipe the mousse into serving glasses or bowls, dividing evenly.

Chill in the refrigerator for about 30 minutes to firm, if desired, then serve.