In a medium saucepan, cream together 1/2 cup of unsalted butter and 1 cup of granulated sugar until light and fluffy. Add the zest of 2 lemons, 4 large eggs, and 1/2 cup of freshly squeezed lemon juice. Cook over low heat, stirring constantly for about 10–15 minutes, or until the mixture thickens and coats the back of a spoon. Remove from heat and let it cool before refrigerating.

In a heatproof bowl, combine 2 whole eggs, 2 egg yolks, 1/2 cup of sugar, the zest of 1 lemon, 1/2 cup of lemon juice, and a pinch of salt. Place the bowl over a pot of simmering water and whisk continuously for about 8–10 minutes, or until it thickens. Once thickened, remove from heat and allow it to cool before chilling in the fridge.

In a clean stand mixer bowl, add 3 large egg whites and a pinch of salt. Beat on medium speed until soft peaks form, which should take about 2 minutes. Gradually add 1/4 cup of granulated sugar while continuing to beat on high until stiff peaks are achieved, approximately 4–5 minutes.

Gently fold the beaten egg whites into the chilled lemon filling in two parts, being careful not to deflate the mixture. Once incorporated, add the previously prepared lemon curd, and carefully fold until the mixtures are combined and smooth.

Transfer the combined mousse mixture into individual serving cups or a large serving bowl. Cover with plastic wrap and refrigerate for at least 4 hours, or preferably overnight, to let it set.

Just before serving, beat 1 cup of cold heavy whipping cream in a mixing bowl until it begins to thicken. Gradually add 2 tablespoons of powdered sugar and 1 teaspoon of vanilla extract, and continue beating until soft peaks form.

Spoon the whipped cream generously over each serving of the Fresh Lemon Mousse. Garnish with fresh berries and sprinkle some additional lemon zest on top.