Prep your tools and ingredients. Chill a mixing bowl and whisk or beaters for the whipping cream. Soften the cream cheese and butter to room temperature. Zest and juice the lemons before you begin.

Make the lemon base. In a small saucepan off the heat, whisk together the lemon juice, lemon zest, powdered sweetener, vanilla, and salt. Taste and adjust sweetness now; it should be tart but pleasantly sweet.

Emulsify with butter. Place the saucepan over low heat and add the butter a few cubes at a time, whisking constantly. Keep the heat gentle to avoid curdling or separating. The mixture should look glossy and slightly thickened, like a thin curd, after 3–5 minutes. Remove from heat and let it cool to lukewarm.

Blend with cream cheese. In a medium bowl, beat the softened cream cheese until smooth and fluffy, about 1 minute. Gradually beat in the lukewarm lemon mixture until fully combined and silky. If you see tiny lumps, keep mixing; they’ll smooth out as the temperatures equalize.

Whip the cream. In the chilled bowl, whip the heavy cream to medium-stiff peaks. It should hold shape but still look satiny. Avoid overbeating; grainy cream will make the mousse dense.

Fold to finish. Add one-third of the whipped cream to the lemon-cream cheese mixture and gently fold to lighten. Fold in the remaining whipped cream in two more additions until no streaks remain.

Portion and chill. Spoon or pipe the mousse into 6–8 small cups or jars. Cover and chill for at least 2 hours to set. The flavors will mellow and bloom as it chills.

Garnish and serve. Right before serving, top with a pinch of lemon zest, a couple of raspberries, or a mint sprig for color and freshness.