In a large pan add brown sugar and butter; cook over low heat until sugar dissolves and mixture is bubbly - approximately 1 –2 minutes. Add salt and nutmeg. Increase heat to medium; add pears and cook for approximately 10 minutes, stirring constantly. Remove from heat and set aside. Preheat the oven. Spread butter equally onto bread slices. Arrange in a single layer on a baking sheet; cook until toasted. Turn bread over and toast other side. In a medium bowl combine arugula and shallot slices. Drizzle with oil and vinegar; sprinkle with pepper; toss to evenly coat. Place one Castello Blue Cheese Slice on each bread slice. Divide arugula mixture evenly on top of the cheese, then with prosciutto slices. Top with caramelized pears and serve.