Combine flour, salt and pepper in bag. Slice the liver into 1/2 inch strips and shake in bag of seasonings to coat. Set aside. Heat skillet with 2-3 tablespoons of butter and a dash of oil. Saute the onions on medium heat until tender and glossy. Transfer to side dish and sprinkle with sage, salt and pepper. Return skillet to high heat, add 3-4 tablespoons butter and dash of oil. Add liver and sear 5 minutes until brown. Inside meat should be slightly pink. Return onions to pan til heated. Remove liver and onions from pan and plate. Use stock and wine to deglaze pan and reduce liquid til you have a thickened sauce. Pour over liver and onions, sprinkle with parsley and serve.