Begin by zesting the lemons using a microplane to capture those fragrant oils, then juice them to extract the vibrant flavor. Set aside the zest for garnish later.

In a medium saucepan, whisk together the egg yolks and granulated sugar until smooth. Gradually stir in the freshly squeezed lemon juice, then place the saucepan over low heat. Gently cook while stirring constantly for about 5–7 minutes, until the mixture thickens enough to coat the back of a spoon.

In a small bowl, sprinkle the gelatin powder over the cold water and let it bloom for about 5 minutes. Once bloomed, gently dissolve the gelatin over low heat for 2–3 minutes, stirring until fully melted. Let it cool slightly before incorporating it into the warm custard.

In a separate chilled mixing bowl, pour the heavy cream and add the vanilla extract. Use an electric mixer to whip the cream on medium speed for about 2–3 minutes until soft peaks form.

To lighten the lemon custard, fold in one-third of the whipped cream until just combined. Next, gently fold in the remaining whipped cream with a spatula, taking care not to deflate the airy texture.

Spoon or pipe the light lemon mousse into individual serving glasses. Once filled, cover the glasses with plastic wrap and chill in the refrigerator for at least two hours.

Once chilled and set, remove the lemon mousse from the refrigerator. Just before serving, sprinkle the reserved lemon zest on top to add color and aroma.