Bring a small pot of water to a boil.
Place a medium-size pot over medium-high heat and melt the butter. Sprinkle the flour over the melted butter and cook for about 1 minute. Slowly whisk the milk into the butter-flour mixture. Season with nutmeg, salt, and ground black pepper and cook for about a minute until it thickens up. Remove from heat and stir in the cheese and rosemary ham in a figure-eight motion. Let cool slightly.
While the sauce is cooling, salt the boiling water and cook asparagus until cooked through but still firm. Remove from the water and slice into pieces on an angle.
Lay the pastry dough out onto nonstick baking sheet. Spread the cheese and ham sauce evenly over the dough then top with the asparagus and sprinkle with cheese.