In a 12-inch non-stick skillet, melt butter; add onions and sauté over medium heat for 5-7 minutes. Stir in sugar and grind some fresh black pepper over the onions, stir to mix, cover, reduce heat to low and cook an additional 20 minutes, stirring once or twice.
Meanwhile, rinse turnip greens, drain in colander and microwave in a covered container for 15 minutes, stirring once halfway through.
When onions are done, stir turnips into onions, heat through, and season with a few squirts of hot pepper sauce, to taste. Pass the bottle of hot pepper sauce at the table for people who like it extra spicy.