Spray a 7x11-inch baking dish with cooking spray and preheat the oven to 400 F.
Arrange the asparagus in a single layer (if possible) in the baking dish
Make the bechamel sauce: melt 3 tbsp of butter in a large saucepan over medium heat and saute the garlic for 30 seconds. Add the flour and cook it for a couple of minutes until slightly golden brown.
Whisk in the half and half, nutmeg, and pepper, and simmer until it starts to thicken
Remove from heat and stir in ½ cup of Parmesan cheese until melted.
Pour the sauce over the asparagus, leaving a one inch border without sauce. Bake, uncovered, for 8-9 minutes depending on how thick your asparagus are.
Make the crispy topping: melt the remaining tablespoon of butter in a medium-sized bowl and mix in the parsley flakes and breadcrumbs until moistened.
Stir in the remaining ½ cup Parmesan cheese
Remove the asparagus from the oven and sprinkle the topping evenly on top. Return to the oven and bake for an additional 8-9 minutes until golden and crispy on top.