Set up a double boiler with a glass bowl and add the egg yolks, lemon juice and lemon zest, Swerve, and yogurt
Whisk constantly until the mixture thickens into a curd like consistency.
Remove from the heat and set aside, stirring occasionally as it cools.
Whisk the egg whites until they form stiff peaks.
When the lemon curd mix has cooled completely, fold it into the egg whites gently until combined.
Pour mousse into ramekins and refrigerate for at least 2 hours.
In a medium bowl, beat the cream, vanilla extract, and Swerve until stiff peaks form.
Serve the mousse topped with a dollop of whipped cream.