Put the gelatin sheets in cold water for 5-10 minuts.
Wisk eggs and sugar until you have a very airy mixture. Use an electric mixer.
Grate the peel of the lemon finely (you need 1 tbsp. of lemon zest) and squeeze the juice out of the lemons (you'll need 1 dl. lemon juice).
Press the geletin sheets in your hands to get the water out. Place it in a saucepan with 2 tablespoons of the lemon juice. Heat at low temperature until the geletin is completely melted. Keep stiring when heating.
When the geletin is melted, remove the pan from the heat and add the remaining lemon juice and the grated lemon zest. Now gently mix in the lemon juice with geletin and lemon zest into the airy egg mixture.
Whip the cream until semi stiff peaks. Carefully mix the whipped cream into the egg/lemon mixture while saving some whipped cream for garnish (about 1 dl). Arrange your lemon mousse in a large bowl or in smaller serving glasses. Let the mousse set for 2 hours in the fridge, and garnish with a little whipped cream on top.