Lasagna Rolls

INGREDIENTS

• 1 to 2 tablespoons olive oil
• 1 cup shredded mozzarella (about 4 ounces)
• 1 cup plus 2 tablespoons grated Parmesan
• 1 (15-ounce) container whole milk ricotta cheese
• 1/4 teaspoon salt
• 3 ounces thinly sliced prosciutto, chopped
• 3/4 teaspoon salt, plus more for salting water
• 12 uncooked lasagna noodles
• 1 large egg, beaten to blend
• 2 tablespoons unsalted butter
• 1/8 teaspoon ground black pepper
• 1 1/4 cups whole milk
• 1/2 teaspoon freshly ground black pepper
• 4 teaspoons all-purpose flour
• Pinch ground nutmeg
• 2 cups marinara sauce
• 1 (10-ounce) package frozen chopped spinach, thawed, squeezed dry