In a small saucepan, melt the butter over low heat. Just enough to melt it.

Set it aside to cool off.

Preheat the oven to 325° Fahrenheit or about 160° Celsius. Place a dish filled with water inside the oven.

Prepare the baking dish. For best results, use springform baking pan. Line the bottom with parchment paper, and using ½ teaspoon of butter, lightly grease the sides.

Using two bowls, separate the egg yolks from the egg whites.

Using a hand mixer, beat the egg whites with half the portion of sugar until firm and stiff.

Beat the egg yolks with the remaining portion of sugar, vanilla, lemon juice and/or lemon zest.

Once the egg yolks obtain a creamy, whitish, and smooth texture, slowly add the cream cheese, cup by cup. Keep mixing until all combined. To remove the extra air bubbles, gently tap the bowl several times on the countertop so that the bubbles float to the surface and pop.

Next, add the mascarpone cheese and continue mixing.

Slowly add the melted butter as you continue mixing, and until you obtain a creamy uniform batter.

Add the egg whites, and using a spatula, gently mix until just combined.

Add potato flour and continue mixing.

Once all combined, pour the batter into the baking pan.

Bake for 50 - 55 minutes. Do not open the oven door while the cheesecake is baking.

Once the cheesecake is baked. Turn off the oven and crack open the oven door. Let the cheesecake cool off gradually while still inside the oven for about 30-45 minutes.

Remove the cheesecake from the oven and let it cool for another hour. You might notice few cracks, but don't worry about those. They can be covered up with an appetizing topping.