Cream together 1/2 cup of unsalted butter and 1 cup of granulated sugar in a medium saucepan over low heat. Stir in zest of 2 lemons, a pinch of salt, 3 eggs, and 1/2 cup of lemon juice. Cook until thickened, about 8 minutes, then cool and refrigerate.

In a heatproof bowl, whisk together 3 eggs, 1/2 cup of granulated sugar, zest of 2 lemons, 1/2 cup of lemon juice, and a pinch of salt. Warm over simmering water for about 12 minutes to thick custard consistency, then chill.

In a clean bowl, whip 3 egg whites with a pinch of salt until soft peaks form. Gradually add 1/4 cup of sugar and whip to stiff peaks, about 3-5 minutes.

Gently fold the whipped egg whites into the chilled lemon filling, then add the chilled lemon curd and fold until well-combined.

Transfer the mixture into serving dishes, cover, and refrigerate for at least 4 hours until set.

Whip 1 cup of heavy whipping cream with 2-3 tablespoons of powdered sugar and 1 teaspoon of vanilla until soft to medium peaks form for garnish.

Once set, top with whipped cream and optionally garnish with lemon zest or fresh berries. Serve chilled.