Preheat oven to 400 F. In a large skillet cook onions in hot oil 5 minutes over low heat; season with salt and pepper. Add 2 tablespoons of the butter and garlic; cook 8 minutes more or until onions are tender. Remove from heat; set aside.
Grease 10 to 12 (5- to 7-ounce) baking dishes with the remaining butter. In bowl, combine eggs and milk; whisk in flour. Add cheese and the snipped sage; combine. Spoon onion in dishes; pour egg mixture over. Bake 20 to 25 minutes or until puffed and golden. Remove; let stand 10 minutes. Serve warm with fresh sage leaves. Serves 10 to 12.