In a large bowl with an electric mixer (or in a stand mixer) whip the heavy cream until stiff peaks form. Transfer to a separate bowl.
Whip the cream cheese, sweetener, and lemon extract until light and fluffy. Add 1/3 of the whipped cream and mix well.
Gently fold in the remaining whipped cream. Pipe or spoon into small serving bowls. Garnish with lemon zest, if desired.
Notes
Lemon juice will not work for this recipe. The amount you need for a vibrant lemon flavor will make the mousse too thin. You need to use lemon zest or lemon extract.