Place the cottage cheese, peanut butter, sweetener, vanilla extract, and salt into a high-speed blender or food processor.
Blend on high for 30 to 60 seconds until the mixture is completely smooth and no curds remain.
If the mousse is too thick, add 1 tablespoon of milk or cream and pulse until the desired consistency is reached.
Transfer the mousse to serving bowls or small jars.
Refrigerate for at least 15 minutes to allow the mousse to set and flavors to meld.
Serve topped with crushed peanuts or dark chocolate chips if desired.