Asparagus Casserole

Bahan-bahan (8 porsi)

• 2 lbs asparagus (trimmed)
• 4 Tbsp unsalted butter (divided, plus more to grease casserole)
• 2 1/2 Tbsp all-purpose flour
• 2 cups half and half ((or equal parts milk and heavy cream))
• 2 tsp garlic salt
• 1/4 tsp black pepper
• 1 cup parmesan cheese (divided)
• 1/2 cup Panko bread crumbs