Without turning on the heat, whisk the eggs in a medium saucepan until frothy.
Juice the lemons and whisk the juice into the eggs.
Slowly whisk in 1 cup of broth.
Turn heat on medium and continue whisking until the sauce begins to thicken.
Mix starch with some of the remaining 1/2 cup of broth to make a paste, and then mix in the rest of the broth.
Slowly whisk the tapioca mixture into the pot on the stove until it thickens up. Turn off the heat, season with salt and black pepper to taste, add a drizzle of extra virgin olive oil (optional), and serve.
Notes
*Broth:
if you happen to be making Lahanodolmades, the broth from steaming them is amazing in this recipe, and it's totally fine to add it hot, straight from the pot. Otherwise, use chicken broth or vegetable broth.
you can add up to 2 cups of broth (475ml) if you like your sauce runnier.