Place a mesh strainer over a bowl, and set aside. In a medium saucepan, whisk together the lemon juice, sugar, egg yolks, eggs, and salt. Add the butter cubes and set the pan over low heat, whisking constantly until the butter is melted. Increase the heat and cook over moderate heat, whisking constantly, until the mixture thickens and just begins to become jelly-like. It’s done when you lift the whisk and the mixture holds its shape when it falls back into the saucepan from the whisk. Immediately press the curd through the strainer. Once strained, store the lemon curd in the refrigerator. It will keep for up to one week.