Preheat and prepare: Preheat oven to 350°F and spray a 9×13 inch casserole dish with cooking spray.: The oven temperature should feel consistent and even, a warm 350°F that encourages gentle bubbling rather than aggressive boiling. You'll notice the kitchen begin to smell faintly of warm air as the oven comes to temperature. Preparing a 9x13 inch casserole dish with cooking spray ensures the edges release cleanly after baking, avoiding sticky patches. One tip, let the oven fully reach 350°F before placing the dish inside, because inserting too early can lead to uneven cooking. A common mistake is skipping the spray; this can make serving difficult when bits cling to the dish.
Make sauce: In a large, oven-safe skillet, brown 1 pound Italian sausage. Drain grease from skillet. Add 1 jar marinara sauce, salt and pepper and 1 teaspoon Italian seasoning. Scoop out about 1/2 of the sauce and set aside.: When you brown the 1 pound Italian sausage in a large, oven safe skillet, listen for an energetic sizzle and watch the meat develop mahogany brown edges, which signal deep, savory flavor. Draining the grease reduces excess oil that could weigh down the casserole, while leaving a little bit helps carry flavor into the sauce. Adding the jarred 28 ounce marinara sauce , plus salt, pepper, and 1 teaspoon of Italian seasoning , creates a rich, fragrant pool that will infuse the ravioli. Scoop out about half of this sauce and set it aside; having reserved sauce keeps the layers balanced and prevents the top from becoming overloaded. Avoid undercooking the sausage, which leaves a raw texture, and be careful when draining not to pour off all flavorful drippings.
Make cheese layer: In a medium sized mixing bowl, add 1 cup ricotta, 2 tablespoons chopped, fresh parsley, 1/2 teaspoon garlic powder, 1 teaspoon Italian seasoning and 1/4 cup parmesan cheese. Stir well.: In a medium mixing bowl combine 1 cup ricotta cheese with 2 tablespoons chopped fresh parsley , 1/2 teaspoon garlic powder , 1 teaspoon Italian seasoning , and 1/4 cup grated parmesan cheese . As you stir, the mixture should feel dense yet spreadable, the herbs brightening the pale ricotta. This mixture forms a creamy cushion that contrasts the pasta and sauce. If the ricotta seems grainy, a vigorous stir or a brief whisk will smooth it. A common pitfall is over thinning this mix with liquid, which can make the layer sink during baking.
Layer: Add the frozen ravioli to the top of the sauce. Add all the cheese mixture to the top of the ravioli and gently spread. Cover with the remaining sauce and finish with the 2 cups of mozzarella.: Add the frozen cheese ravioli on top of the sauce in the skillet or dish so they sit snugly in the first sauce layer, which helps them cook evenly and absorb flavor. Spoon all of the cheese mixture onto the ravioli and gently spread so each piece gets a covering, taking care not to tear the ravioli. Pour the reserved sauce over the cheese layer to lock in moisture and finish with 1 to 2 cups of shredded mozzarella cheese for a luxurious top. You'll see a contrast between the pale cheese layer and the bright red sauce before baking. Avoid piling too much cheese in one area as that can insulate sections and prevent even bubbling.
Bake: Bake uncovered for 45 minutes and let sit for 15 minutes before serving.: Bake uncovered for 45 minutes until the edges of the sauce bubble vigorously and the top of the mozzarella cheese is melted and showing hints of golden brown. The sound in the oven will be a gentle, steady simmer as steam escapes, and visually you'll notice small pockets of sauce rising around the ravioli. After removing from the oven, let the casserole sit for 15 minutes to set; this rest makes slicing neater and allows the interior to thicken. A key mistake to avoid is serving immediately, which can result in runny portions and lost structure.