In a heavy skillet, melt butter. When foam subsides, add the bacon and fry for 5 to 10 minutes or until the bacon is lightly browned. Remove bacon from skillet and set on paper towel lined plate to drain.
In same skillet used for bacon, fry the onion slices for 6 to 8 minutes adding more butter as necessary. When the onions are soft and transparent, add the apple rings.
Put lid on skillet and simmer apples over low heat for 5 to 10 minutes. Carefully stir apples to keep them from sticking. When the apple rings are done, they should offer little or no resistence when pierced with the tip of a sharp knife, return the drained bacon to the skillet.
Cover skillet and simmer an additional 3 to 5 minutes or until the bacon is heated through. Liberally grind fresh black pepper over the top and serve immediately.