Preheat the oven to 425ºF. Spray a 9x13 pan (ceramic, glass, or metal) with cooking spray or a light layer of oil. You'll also want to have a piece of aluminum foil ready for the top of the pan.
Combine the chicken stock, heavy cream, marinara sauce, garlic, salt, oregano, and sugar in a large microwave-safe bowl or liquid measuring cup. Microwave the mixture until very hot, about 5 minutes, pausing to stir occasionally.
3 cups chicken stock, 1 cup heavy cream, 1 (22-24 ounce) jar marinara sauce, 1 tablespoon minced garlic, 1 teaspoon kosher salt, 1 teaspoon dried oregano, ½ teaspoon sugar
While the liquids are warming, pour the ziti noodles into the prepared pan. Pour the hot liquids directly on top, covering evenly.
1 lb ziti pasta noodles
Add dollops of ricotta cheese across the top of the noodles, if using. Then cover tightly with aluminum foil being sure to crimp the edges. Bake for 35-40 minutes, or until the noodles are just about al dente.
8 ounces ricotta cheese
Remove the tinfoil from the top of the pan and sprinkle the mozzarella cheese across the top evenly. Return to the oven and bake for another 10-15 minutes, or until the cheese is melted and the edges are hot and bubbly.
6 ounces (about 1½ cups) mozzarella cheese