Preheat the oven to 300°F (150°C) and prepare an 8-inch round cake pan by lining the bottom with parchment paper and greasing the sides.

In a heatproof bowl, combine the cream cheese, butter, and heavy cream. Set the bowl over simmering water and stir gently for about 5-7 minutes until smooth, then cool slightly.

Whisk in the egg yolks until fully incorporated. Sift in the cake flour and add lemon zest and vanilla extract to form the batter.

In a separate bowl, whip the egg whites until frothy, add lemon juice, then gradually sprinkle in sugar until medium-soft peaks form.

Gently fold the whipped egg whites into the batter in three increments.

Pour the batter into the prepared pan, smooth the top, and tap gently on the counter to release air bubbles.

Place the cake pan in a larger roasting pan filled with hot water to create a water bath.

Bake for 80-90 minutes until golden and a skewer inserted comes out clean.

Turn off the oven and leave the door ajar to cool for about 30 minutes.

Run a knife around the edge, invert onto a plate, and allow to cool completely before slicing.