Manicotti with Homemade Ricotta

Name: Manicotti with Homemade Ricotta
Ingredients: 6 large eggs; 1¼ cups all-purpose flour; ½ tsp. kosher salt; Nonstick vegetable oil spray; 7 cups whole milk; 1 cup heavy cream; 3 tsp. salt; 5 Tbsp. distilled white vinegar; 2 large egg yolks, beaten to blend; 1½ lb. ricotta; 8 oz. mozzarella, grated; 1 oz. Parmesan, grated, plus more for serving; 2 10-oz. frozen chopped spinach, thawed, drained (optional); Kosher salt, freshly ground pepper; 3 cups marinara sauce, preferably homemade, divided