1. Prepare the liver: Trim any connective tissue or membrane from the 21 ounces beef liver. Slice the liver into 1/4-inch–thick pieces for even cooking.

2. Soak in buttermilk: Place the liver slices in a shallow dish and pour 3/4 cup buttermilk over them. Cover and refrigerate for at least 1 hour (or up to overnight) to tenderize and mellow the flavor.

3. Drain and pat dry: Remove the liver from the fridge, drain off excess buttermilk, and gently pat each slice dry with paper towels.

4. Season: Lay the liver slices on a plate and sprinkle both sides with 2 teaspoons salt and 1/2 teaspoon black pepper.

5. Flour dredge: Pour 1/4 cup all-purpose flour into a shallow bowl or plate. Dredge each seasoned slice in the flour, shaking off any excess to ensure a light, even coating.

6. Heat the pan: Warm a large skillet over medium-high heat. Add 1 tablespoon olive oil and 2 tablespoons butter. Swirl the pan until the butter foams and froths slightly.

7. Pan-fry the liver: Gently place the floured liver slices in the hot skillet in a single layer. Cook for 2–3 minutes on the first side, until golden brown at the edges. Flip and cook for another 1–2 minutes, aiming for a slightly pink center—overcooking will toughen the liver.

8. Rest the liver: Transfer the cooked slices to a plate and tent loosely with foil to keep warm while you sauté the aromatics.

9. Sauté onions and garlic: In the same skillet, add the sliced onion strips and minced garlic. If the pan looks dry, add a touch more butter. Cook over medium heat for 4–5 minutes, stirring often, until the onions are soft and beginning to caramelize.

10. Combine and finish: Return the liver slices to the skillet and gently toss with the onions and garlic for about 1 minute, just long enough to reheat the liver and coat it in the aromatic pan juices.

11. Plate and serve: Arrange the liver and onions on a serving platter. Optionally garnish with chopped fresh parsley or a squeeze of lemon juice.