In a heavy-bottomed saucepan, combine the lemon juices, zest, sugar, butter, and salt. Stir gently over low heat until the butter has melted and sugar has dissolved.

In a medium bowl, whisk together the eggs and egg yolks. Whisking constantly, gradually add half the hot lemon mixture into the eggs, then slowly whisk the egg mixture back into the remaining lemon mixture. Cook over low heat, scraping the bottom constantly, until the mixture thickens, about 5-7 minutes. Do not allow to boil. Pour the curd through a fine-mesh sieve set over a medium bowl. Cool to room temperature, cover, and refrigerate. Curd can be kept in an airtight container in the refrigerator for up to a week. Enjoy!