This one takes people way back. Old-school, savory, and still a comfort classic for a reason

Prepare the onions: Peel and thinly slice the onions. Set them aside. Pat the liver slices dry with paper towels so the flour will cling better.
Season and flour the liver: Sprinkle the liver on both sides with about 1 teaspoon of the salt and a good pinch of black pepper, if using. Place the flour in a shallow dish and lightly dredge each slice of liver, shaking off the excess. You want a thin coating, not a heavy crust.
Cook the onions: In a large, heavy skillet (cast iron if you have it), melt 2 tablespoons of the butter over medium heat. Add the sliced onions and a small pinch of salt. Cook, stirring occasionally, until the onions are soft, golden, and starting to caramelize around the edges, 12–15 minutes. If they brown too quickly, lower the heat. When done, push the onions to one side of the skillet or transfer them to a plate and keep warm.
Cook the liver: Add the remaining 2 tablespoons butter to the empty side of the skillet (or back into the skillet if you removed the onions). Increase the heat slightly to medium-high. When the butter is hot and foaming, lay the floured liver slices in a single layer. Cook without moving them for about 2–3 minutes, until the underside is nicely browned.
Turn and finish: Flip the liver slices and cook another 2–3 minutes, just until the centers are still slightly pink but not raw. Overcooking will make the liver tough, so watch it closely. Taste a small piece and adjust salt and pepper if needed.
Combine and serve: Return the onions to the pan if you set them aside, nestling them around and over the liver. Let everything warm together for a minute, scraping up any browned bits from the bottom of the skillet. Serve the liver topped generously with the onions, spooning the pan juices over each plate.
Variations & Tips