Whisk the granulated sugar, whole eggs, and egg yolks together in a heat‑proof bowl until well combined.

Transfer the bowl to a saucepan over medium heat and whisk constantly until the mixture thickens slightly, about 5 minutes.

Remove the saucepan from heat and whisk in the butter pieces, lemon juice, lemon zest, and vanilla extract until smooth and glossy.

Strain the curd through a fine sieve into a clean bowl to remove any settled egg bits.

Pour the lemon curd into a jar, cover, and refrigerate for at least 1 hour to set fully. Store in the refrigerator for up to 2 weeks.