1. In a small bowl, soak the gelatin in the water, leaving approximately 10 minutes.
2. At this time, melt the butter in a saucepan. Remove from heat, add sugar, salt, lemon juice and zest. Mix the egg yolks and hammer, beat and put on a small fire, stirring occasionally.
3. Cook until thick (about 8-10 minutes). In no case do not bring to a boil, otherwise the mixture will curdle. If steam starts to go, as before boiling, then remove from heat for 20 seconds, cool slightly and return to the fire.
4. As soon as the mixture thickens, stir in gelatin.
5. Cool the mixture to room temperature, stirring occasionally.
6. Cream whisk until stable peaks with sugar, half of which enter into mousse, mix gently to the cream is not settled.
7. Spread the mousse between 4-6 kremanki, top with remaining cream.