Bifes Com Azedas (Sorrel and Spinach Steaks)

1 1/2 pound round steak, ground
2 pounds spinach
salt and pepper, to taste
butter, to taste
2 tablespoons chopped sorrel
lard or butter for frying
8 egg yolks, poached

1. Wash spinach thoroughly, or if packaged, rinse with water. Put in saucepan without water. Sprinkle with salt and cook gently, uncoverd, until greens are throroughly wilted and tender. Drain well and force through a food mill or fine sieve. Reheat and season with salt, pepper and butter to taste. Add Sorrel to spinach.
2. Season ground steak with salt and pepper and divide and shape into 8 patties with a depression in the center of each. Pan fry in hot lard. Reheat spinach mixture. Divide spinach mixture into 8 parts and arrange a steak patty on top of each . Put a poached egg yolk in the center of each patty. Serve with the pan juices.