Rinse the liver slices under cold water and pat dry with paper towels. Trim away any connective tissue or membranes. If slices are thick, cut into 1/2-inch pieces. Season both sides lightly with 1/2 teaspoon salt, 1/2 teaspoon black pepper and 1 teaspoon garlic powder. Place the flour in a shallow dish and dredge each liver slice, shaking off excess.

Cook bacon

In a large skillet over medium heat, add the bacon slices. Cook until crisp but still pliable, about 6–8 minutes, turning occasionally. Remove bacon to a paper towel–lined plate and reserve 1–2 tablespoons of rendered bacon fat in the skillet (discard excess or reserve for another use).

Sauté onions

If needed, add 1 tablespoon of butter or oil to the bacon fat in the skillet and raise heat to medium-high. Add the sliced onion and a pinch of salt. Sauté, stirring occasionally, until the onion is soft and golden brown, about 8–10 minutes. Push the onions to the side of the pan or remove briefly to a plate while you cook the liver.

Pan-fry liver

Wipe the skillet if it has burned bits but keep leftover fat for flavor; add remaining 1 tablespoon butter and 1 tablespoon oil and heat over medium-high. When hot but not smoking, add the dredged liver in a single layer without crowding (work in batches if necessary). Cook liver 1.5–2 minutes per side for medium (do not overcook or it becomes tough). Transfer cooked liver to a plate and tent loosely with foil.

Make pan sauce and finish

Reduce heat to medium, add red wine (if using) to deglaze the pan, scraping up browned bits. Let wine reduce for about 1 minute, then add the stock and apple cider vinegar. Bring to a simmer and cook until slightly reduced and saucy, about 3–4 minutes. Return onions and chopped bacon to the pan and stir to coat. Taste and adjust seasoning with remaining salt and pepper. Sprinkle chopped parsley over the mixture and remove from heat. Return liver to the pan just to warm for 30 seconds, then serve.

Mashed Potatoes

Place peeled and quartered potatoes in a pot and cover with cold salted water. Bring to a boil over high heat, reduce to a simmer and cook until potatoes are very tender, 15–18 minutes. Drain well and return to the hot pot for 1 minute to dry out lightly.

Mash potatoes with butter using a potato masher or ricer. Gradually add warm milk until you reach the desired consistency. Season with 1 teaspoon salt and 1/2 teaspoon black pepper. Keep warm until ready to plate.

Fresh Vegetables

Steam or blanch mixed vegetables until crisp-tender (carrots and green beans about 4–6 minutes, broccoli 3–4 minutes). Drain and toss with olive oil, 1/2 teaspoon salt and 1/4 teaspoon black pepper. Keep warm.