Mustard Green Gratin: Reloaded - Alton Brown

Ingredients

• 2 tablespoons kosher salt, divided
• 4 tablespoons unsalted butter, divided
• 1 cup crushed buttery crackers (We used 20 Ritz crackers)
• 3/4 cup freshly ground Parmesan cheese, divided
• 1 pound mustard greens, stemmed
• 1/4 cup dry sherry (NOT "cooking" sherry)
• 12 ounces cremini mushrooms, sliced 1/4-inch thick
• 5 large garlic cloves, minced, divided
• 1/2 large yellow onion, chopped
• 1/4 cup all-purpose flour
• 3 cups whole milk
• 1 teaspoon smooth Dijon mustard (Pardon me but do you have...)
• 1 tablespoon hot sauce (We used Pete's)
• 1/2 teaspoon freshly ground nutmeg
• 1/2 teaspoon freshly ground black pepper