Add milk to a shallow bowl. Soak liver in the milk for about 20 minutes to remove any bitterness.
Meanwhile, cook your bacon in a large skillet. Drain on paper towels and cut into 1/2" chunks. Set aside.
Reserve 1 1/2 tablespoons of bacon grease and add 2 tablespoons of the butter to the bacon grease in the same skillet. Add onions and cook over a medium heat stirring occasionally until caramelized, about 25 minutes. Remove onions to a dish, sprinkle with salt and set aside.
Pat liver dry and discard the milk. Return skillet to high heat and add the remaining 3 tablespoons of butter to the pan. When the butter foam subsides, the butter is hot enough. Arrange the liver in the pan being certain not to crowd the pan. I worked in two batches. Sauté for 3 minutes regulating the heat so that the butter remains hot, but does not burn. Turn liver over and sauté about 2 minutes more. The inside meat should still be pink.
Serve liver topped with onion and bacon.
First, cut the liver into strips and soak them in milk to remove any bitterness.
Cooking time depends on how thick your slices are. Don't overcook it or it can become tough.
If you're following a low-carb diet, you may choose to eliminate the onions for an even lower carb count.