Melt butter in small frying pan over low heat. Add pecans and brown sugar. Cook 2 to 3 minutes, stirring constantly until mixture is caramelized. Spread out on wax paper to cool. In a bowl toss together spinach, pecans, apple and cheese. Add oil and vinegar and toss again until everything is coated. Note: To make ahead for a special dinner, toss apple with dressing. Layer on greens, cheese, and pecans. Cover with plastic wrap and put in refrigerator until needed, tossing just before serving.