Wash and dry the lemons thoroughly. Roll them several times on the counter, pressing down to soften them.

Grate the zest and squeeze the juice from them.

Place the zest, lemon juice, sugar, and butter in a heatproof bowl (e.g., metal) and set it over a pot of boiling water.

Heat until the sugar and butter dissolve.

In a bowl, whisk the eggs and egg yolk with a fork.

Add the eggs to the bowl and cook, stirring constantly, until the mixture thickens and becomes velvety smooth.

Strain the finished cream through a sieve to remove any lemon or egg pieces.

Set aside to cool.

Blend the sponge cakes into a powder, or crush them very thoroughly - e.g., with a rolling pin.

Add the melted butter and mix.

Line the baking pan with baking paper.

Spread the sponge cakes on the bottom and press down firmly.

In a mixer bowl, put the quark cheese, add eggs, sweetened condensed milk, lemon juice, and pour in the jelly powder - blend until combined.

Pour the cheesecake mixture onto the sponge cake base.

Place in an oven preheated to 150 degrees Celsius (top/bottom mode) and bake for about 1.5 hours.

After baking, turn off the oven, slightly open the door, and leave the cheesecake inside to cool.

Refrigerate the cheesecake to chill.

Whip the cold heavy cream until thick.

Add roughly half of the lemon curd and gently mix - taste it, if you want, add more lemon curd.

Pour a little cold water over the gelatin - just enough to cover it - mix and let stand for 5 minutes.

Briefly heat the gelatin - I do it in the microwave - usually less than 10 seconds.

Add a tablespoon of cream to the heated gelatin and mix.

Pour the prepared gelatin into the rest of the lemon mousse and mix thoroughly.

Spread the mousse over the cheesecake, smooth the surface, and put it back in the refrigerator for at least an hour.

Before serving, decorate the cheesecake with the remaining lemon curd.