If you are using buttermilk, soak the liver in it for 1 hour ahead of time.
After the hour is up, pat the liver dry and season with salt, pepper, and paprika.
Lightly sprinkle both sides of the liver with flour then shake off any excess flour.
Heat your skillet, add melted butter, and cook the liver 3-4 minutes or until a nice golden brown crust develops.
Flip and continue cooking on the other side for 3-4 minutes or until cooked through.
Set the liver aside to rest, then add oil and onions to the skillet. Cook 4-6 minutes, stirring frequently, until soft.
Top the liver with the fried onions and serve immediately.
Notes
Cooked beef liver doesn't store well, so I recommend making just enough to enjoy immediately.
In this recipe, we are cooking the beef liver very much like a steak. When the liver is ready to be flipped, it should pull away easily from the skillet. If it sticks, try letting it cook a bit longer.
Beef liver cooks best on medium to high heat. Slow cooking liver leads to dry, tough meat.
If you want to use a thermometer to know when your liver is done, aim for an internal temperature of 160°F. Avoid overcooking your liver as it will negatively affect the texture.