Start by slicing the liver into 1/2-inch thick slices. Rinse well and move the sliced liver to a large bowl. Cover with cold water and refrigerate for 24 to 48 hours, changing the water 2 or 3 times.
Once you are ready to fry the liver, heat ½ inch of vegetable oil in a cast-iron skillet over medium-high heat. You are shooting for 325 to 350 degrees oil temperature.
While the oil heats, mix the dredge ingredients in a shallow dish. Dredge each liver slice to coat entire surface well with the seasoned flour. Move the dredged pieces to a wire rack and continue until all liver slices are coated with the flour mixture.
Dredge the sliced liver in seasoned flour.
When the oil is hot enough, slowly lower two or three slices into the oil, being careful not to overcrowd the pan. Fry on each side for 4 to 5 minutes or until golden brown. Move the fried liver to a warm platter and continue until entire batch is fried. Loosely tent the fried liver slices with foil to keep them warm.
Fry the liver to a golden brown, about 4 minutes per side.
Drain all but 3 to 4 tablespoons of oil from the pan. Return the skillet to the heat and add the thinly sliced onions. Sauté the onions for 5 to 8 minutes or until they are softened and slightly golden brown. Sprinkle 3 tablespoons of the remaining flour dredge over the onions and stir well.
Add flour to the softened onions and cook until it takes on a deep tan color.
Continue cooking until the flour begins to lightly brown, another 3-5 minutes. Pour in the beer or chicken stock and bring the mixture to a boil. Reduce heat to a simmer and stir till the gravy thickens.
Add 12 ounces of beer or chicken stock to the hot pan.
Return the liver slices to the skillet and spoon the onion gravy over the top before serving.