01 -
If using the milk soak, place beef liver in a shallow food-safe dish, add milk, cover, and refrigerate for 20–30 minutes. Do not soak on the counter. This optional step does not replace safe cooking.
02 -
Melt 2 tablespoons butter in a broad skillet over medium heat. Cook separated onion rings until soft and lightly colored, about 10–15 minutes or as needed. Transfer to a clean dish before cooking liver.
03 -
Season some flour on a shallow plate. Drain liver, discard milk, and pat slices dry. Coat lightly in flour and shake off excess. Discard flour that has contacted raw liver.
04 -
Use the remaining 2 tablespoons butter to cook liver in uncrowded batches, dividing the butter as needed. Turn when the coating sets and browns; reduce heat if it darkens too quickly.
05 -
Check each slice from the side with a suitable thermometer. Cook the center to 160°F. Remove finished slices to a clean plate and return onions only long enough to heat through.
06 -
Serve promptly with ready side dishes. Refrigerate leftovers within 2 hours, or 1 hour above 90°F, in shallow containers. Reheat saved portions to 165°F throughout.