In a large mixing bowl, stir together the egg yolks, ricotta, sugar and lemon zest. Stir in the flour. In another bowl, beat the egg whites until stiff but not dry; fold a third at a time into the ricotta mixture.
Heat a drizzle of oil (and perhaps a bit of butter) in a well-seasoned cast iron skillet (or any pan you want to use) set over medium heat. Scoop about 1/4 cup of the batter into the pan, spread it out a bit and let it cook until golden on the bottom (bubbles won't rise to the surface as readily with these), then flip and cook on the other side until golden and cooked through.