Place the cottage cheese, cocoa powder, sweetener, vanilla extract, and sea salt into a high-speed blender or food processor.
Process the mixture on high speed for 60 to 90 seconds until the texture is completely smooth and no visible cottage cheese curds remain.
Stop the motor and scrape down the sides of the vessel with a rubber spatula, then blend for an additional 10 seconds to ensure a uniform consistency.
Divide the mousse evenly into two individual serving ramekins or small glass bowls.
Transfer the containers to the refrigerator and chill for at least 1 hour to allow the mousse to firm up and the flavors to emulsify.
Serve chilled, optionally garnished with fresh raspberries or dark chocolate shavings.