Well, the recipe I have might be even heavier since it has butter in it as well, but here 'tis (in U.S. measurements, sorry):
2 TB water
1 tsp plain gelatin
1/2 cup (1 stick) unsalted butter
3/4 cup sugar
3 TB grated lemon zest
1/2 cup fresh lemon juice
pinch of salt
6 large egg yolks
3/4 cup heavy whipping cream
1. Pour the water into a small bowl, sprinkle the gelatin over the water, and let stand about 10 mins, or until softened. Place the bowl in a larger bowl of hot water, and stir until the gelatin has dissolved and the liquid is clear.
2. Meanwhile, melt the butter in a large heavy saucepan over medium-low heat. Remove the pan from the heat and whisk in the sugar, zest, lemon juice, and salt. Whisk in the yolks until smooth. Cook the mixture, stirring constantly, until it thickens and leaves a path on the back of a wooden spoon when a finger is drawn across it; do not allow the mixture to boil.
3. Remove the pan from the heat, stir in the gelatin mixture, and immediately pour through a strainer into a bowl. Let cool to room temperature, whisking occasionally.
4. Beat the cream with an electric mixer on high speed in a large bowl just until the cream forms stiff peaks. Add the cream to the lemon mixture in 3 batches, gently folding it in with a whisk or a rubber spatula just until blended.
5. Divide the mousse evenly between 4 stemmed glasses. Refridgerate, loosely covered, for at least 2 hrs or up to 2 days, until set and thoroughly chilled. Serve with a dollop of whipped cream on top.
From Luscious Lemon Desserts by Lori Longbotham. A must-have cookbook if you like lemons + sugar as much as I do.