Long and thin, Stir-fried bean sprouts with butter

Natsuki attended the wedding of a high school friend. She was fond of saying "definitely" and said "I will definitely have a garden wedding. However the wedding was more relaxed than Natsuki had expected, and she came home anticlimactic. She paid a lot of congratulatory gifts and had a poor wallet. Today's supper is going to be a economical menu using bean sprouts. And the other star of the dish is....