In a large sauce pot, whisk together eggs and yolks until smooth and homogenous.
Whisk in sugar and salt very well.
Slowly whisk in the lemon juice.
Cook over medium heat, stirring constantly until nappant. Nappant is when you can dip a spoon or spatula into the custard and draw a line across it with your finger and the custard does not run down the spoon into the line.
Remove from heat and stir in butter.
Strain into a bowl or a plastic wrap-lined baking sheet. Cover with plastic wrap, poke a few holes and refrigerate until cold.
Notes
Note: You can omit the butter for a dairy free option. It will still be delicious and smooth. The butter adds a richness and silky mouthfeel.Keeps for a week in the refrigerator.