Prep the lemon. Zest the lemon first, then juice it.
Measure out 2–3 tablespoons of juice. Set aside.
Whip the cream. In a cold mixing bowl, beat the heavy cream to stiff peaks. Don’t overbeat into butter; look for firm peaks that hold their shape.
Set aside.
Beat the cream cheese. In a separate bowl, beat the softened cream cheese until completely smooth and fluffy, about 1–2 minutes. This step prevents lumps.
Sweeten and flavor. Add powdered sweetener, vanilla, salt, lemon zest, and 2 tablespoons lemon juice to the cream cheese. Beat until smooth.
Taste and adjust sweetness and lemon intensity; add more lemon juice or a few drops of lemon extract if desired.
Fold it together. Gently fold the whipped cream into the lemon cream cheese mixture in two or three additions. Use a spatula and light strokes to keep it airy.
Chill or serve. Spoon into dessert cups. Eat immediately for a soft mousse, or chill 30–60 minutes for a firmer, fluffier set.
Finish with toppings. Add berries, extra zest, or a sprinkle of keto cookie crumbs for texture.