In a medium saucepan, combine sugar, eggs, and lemon zest and juice. Cook over medium heat, whisking constantly, until a candy thermometer registers 185°. Press mixture through a fine-mesh sieve into a medium bowl; let cool until mixture registers 113°.
With a mixer at medium speed, add cold butter to curd mixture, beating until smooth. Refrigerate in an airtight container.
Recipe by Louisiana Cookin' at https://louisianacookin.com/black-sesame-pudding/