Prep the liver: Rinse the slices under cold water and pat dry. Trim away any visible membranes. Place in a bowl and cover with milk (or lightly salted water). Soak for 20–30 minutes. This mellows the flavor and helps with tenderness.

Slice the onions: While the liver soaks, thinly slice the onions. A combination of butter and oil helps them soften and brown without burning.

Caramelize the onions: Heat 1 tablespoon butter and 1 tablespoon olive oil in a large skillet over medium heat. Add onions, a pinch of salt, and cook, stirring often, for 12–15 minutes until golden and jammy. Remove to a plate and keep warm.

Season and dredge the liver: Drain and pat the liver very dry. Season both sides with salt, pepper, and smoked paprika. Lightly dust with flour, shaking off excess. This creates a light crust and helps the sauce cling.

Sear the liver: Add the remaining butter and oil to the skillet. Heat over medium-high until shimmering. Lay the liver slices in a single layer (work in batches if needed). Sear 1.5–2 minutes per side, just until browned outside and still slightly pink inside. Do not overcook—it should be tender, not gray and dry. Transfer to a warm plate and tent loosely with foil.

Make the pan sauce: Lower heat to medium. Add the garlic and stir for 20–30 seconds. Pour in the beef stock and Worcestershire, scraping up the browned bits. If you like a thicker sauce, whisk a pinch of flour with a splash of stock, then stir it in. Simmer 2–3 minutes until slightly glossy.

Combine and finish: Return the onions to the pan and toss in the sauce. Add any juices from the resting liver. Taste and adjust seasoning. Nestle the liver back into the skillet for 30–60 seconds to warm through, without cooking it further.

Serve: Sprinkle with parsley and a squeeze of lemon if you like. Serve over creamy mashed potatoes, buttered noodles, or crusty bread to mop up the sauce.