Rinse the ox liver slices under cold water and pat them dry with a paper towel. If desired, remove any membranes or connective tissue from the liver.
In a large frying pan or skillet, heat the vegetable oil and butter over medium-high heat.
Add the thinly sliced onions to the pan and sauté them until they become soft and translucent.
If using garlic, add the minced garlic to the pan and cook for an additional minute, stirring continuously.
Increase the heat to high and add the ox liver slices to the pan. Cook the liver for about 2-3 minutes on each side, or until they are browned on the outside but still slightly pink in the center. Be careful not to overcook the liver, as it can become tough and lose its tenderness.
Season the liver slices with salt and pepper to taste while they are cooking.
Once the liver is cooked to your desired level of doneness, remove it from the pan and transfer it to a serving plate.
Serve the pan-fried ox liver hot, accompanied by the sautéed onions. Squeeze fresh lemon juice over the liver slices for added flavor, if desired.Pan-fried ox liver is often served with side dishes such as mashed potatoes, steamed vegetables, or rice. Enjoy your South African-style ox liver dish!