Zester the lemons to retrieve the zest, then squeeze the lemons to extract the juice.

In a small bowl, soak the gelatin in cold water for about 5 minutes.

In a saucepan, heat the lemon juice with the sugar over low heat until the sugar is dissolved.

Remove the saucepan from heat, then add the squeezed gelatin to the hot lemon mixture. Stir until completely dissolved.

In a mixing bowl, beat the egg yolks. Gradually pour the warm lemon mixture into the egg yolks while whisking to prevent the eggs from cooking.

In another bowl, whip the heavy cream until it forms stiff peaks.

Add the lemon mixture to the beaten egg whites and gently mix. Then fold in the whipped cream.

Pour the mousse into glasses or a mold and refrigerate for at least 3 hours to set.