Combine flour, salt, paprika, and sage in paper or plastic bag.
Cut large livers in half; add 1/3 of the livers at a time; shake to coat well.
In heavy skillet cook onion in 2 tablespoons of the butter till tender but not brown.(Electric skillet 300°.)
Push onion to one side and brown the livers lightly, 5 or 6 minutes.
Push to one side.
Add remaining 1 tablespoon butter and apple slices; cook till tender, about 5 minutes.
Sprinkle apples with sugar to glaze.
Serve with toast.