Whisk the curd base: In a small saucepan off the heat, whisk the eggs, sweetener, lemon juice, zest, and salt until smooth. This helps prevent scrambling once you add heat.

Cook low and slow: Place the pan over low heat. Whisk constantly until the mixture thickens, 6–10 minutes. Don’t rush it. You’re looking for it to coat the back of a spoon.

Add the butter: Remove from heat and whisk in the butter, a few pieces at a time, until fully melted and silky. This gives the curd a lush texture.

Strain (optional): For extra-smooth curd, push it through a fine-mesh strainer into a bowl. Press plastic wrap directly over the surface and chill for at least 1 hour.

Whip the cream: In a chilled bowl, beat the cream, sweetener, vanilla, and salt to soft or medium peaks. Taste and adjust sweetness if needed.

Layer the parfaits: Spoon a layer of lemon curd into each glass, then add a layer of whipped cream. Repeat to fill the glasses. Add berries, nuts, or cookie crumble between layers if you like.

Finish and chill: Top with a final dollop of cream and a sprinkle of lemon zest. Chill 30 minutes for neater layers, or serve right away for a softer set.

Serve: Add a few fresh berries or a crunchy sprinkle right before serving for contrast.