Liver delivers more vitamin A, B12, iron and folate per gram than almost any other food. It is the carnivore equivalent of a multivitamin.
Cook it hot and fast. Slice 1cm thick, season with salt, fry in beef fat for 90 seconds per side. Pink in the middle.
If you can't stomach the texture, blend raw liver into your mince (10-20%) before cooking. You won't notice it.