How We Made Our Rich Lemon Filling
We used ripe, fresh lemons for the juice. We were careful to scrape only the outer peel of the lemon for our zest. (The inner, white layer is bitter.)
Fat is pleasing to the palate, lending a rich mouth feel. So we added an extra egg yolk. And the cooked egg yolks made the filling more firm so that it would hold its shape when cut.