Place the softened cream cheese in a microwave-safe mug or 8-ounce ramekin.

Whisk the cream cheese with a fork or mini-whisk until completely smooth and free of lumps.

Add the egg, sweetener, vanilla extract, lemon juice, and optional heavy cream to the mug.

Whisk the mixture vigorously for 60 seconds until the batter is homogeneous and aerated slightly.

Microwave on high power (1000W) for 60 seconds.

Check the internal consistency; the edges should be set and pulling away from the sides, while the center remains slightly jiggly and glossy.

If the center is still liquid, continue to microwave in 15-second intervals until the jiggly stage is reached.

Allow the cheesecake to rest at room temperature for 10 minutes.

Transfer to the refrigerator and chill for a minimum of 30 minutes. This step is critical for the lipid structure to stabilize and the texture to firm up.

Serve directly in the mug or run a knife around the edge to invert onto a chilled plate.