Put your thawed chicken livers in a container, cover it with buttermilk, add the lid, and let it soak in your refrigerator overnight.
Cook the Chicken Liver Souffle
Preheat your oven to 350℉ (177℃). Heat up your skillet over medium-low heat and add 2-3 tablespoons of cooking fat. (I prefer using rendered sausage fat for this recipe.) Add some of the chicken livers but leave enough space so they're spread out in your skillet. Cook for 4-5 minutes on each side until they are nicely browned. Remove the cooked livers to the food processor or blender. Repeat until all the livers are cooked. Clean out your skillet after it cools down.
Process the chicken livers in the food processor or blender. Pulse-chop in 5-second increments until the livers are small crumbles. Set aside.
Beat your eggs in a medium mixing bowl and combine with the milk. Set aside.
Smear about 1 tablespoon of cooking fat (I use sausage fat again) all around the inside of your clean, cool skillet. Pour the egg mixture inside and add the oats, raisins, salt, and pepper. Add in the chicken liver and 1 ½ cups of the shredded cheese. Stir gently to combine but try not to scrape off the cooking fat.
Melt the butter in a small sauce pan and drizzle over the top of your souffle. Bake uncovered at 350℉ (177℃) for 1 hour. When the timer goes off, sprinkle the remaining ½ cup of cheese on top, and bake an additional 2-3 minutes until the cheese is browned. Serves 8-10 people.