The shells are the part that can turn a cozy bake into a frustrating one: cook them all the way to the package time, and they keep softening under the sauce in the oven. I stop a minute early, which leaves them tender but sturdy enough to fill without splitting. These mushroom and spinach stuffed shells bring together browned mushrooms, wilted greens, and a creamy ricotta filling in a 9×13-inch dish that serves six.
The filling has a little more going on than ricotta and cheese, so the order matters. I let the mushroom and spinach mixture cool until just warm before stirring in the egg and dairy; that gives everything a chance to come together without starting to set the egg. Once the shells are covered in marinara and baked until bubbling, the edges are saucy and the centers stay soft and rich.
Kitchen Note
Press the foil snugly around the baking dish for the covered part of the bake. A loose cover lets the sauce at the edges dry out before the middle is hot.
Save these mushroom and spinach stuffed shells for a cozy baked pasta night, with a creamy filling and bubbling marinara on top.
Why the Mushrooms Need to Brown Before They Meet the Ricotta
Mushrooms carry plenty of water, and that moisture has nowhere to go once it’s folded into the cheese. If they go into the filling before their liquid cooks off, the ricotta mixture can turn loose and leave watery sauce in the bottom of the dish. Give the chopped cremini time in the skillet until they’re browned and the pan looks dry. That change is more useful than chasing extra seasoning: it concentrates their earthy flavor and keeps the filling from getting soupy.
The spinach brings its own moisture, though it cooks down quickly in handfuls. Stir it into the browned mushrooms and let it wilt before you move the mixture to the bowl. You’re not trying to crisp the greens or cook them until they disappear; wilted leaves mixed through the mushrooms give the filling a tender, savory bite. With the vegetables cooked first, the ricotta stays creamy rather than diluted, and the filling is much easier to spoon into the shells.
Why the Ricotta and Mozzarella Make This Filling Hold Together
- Whole-milk ricotta — It gives the filling its soft, creamy base. Whole-milk ricotta tastes richer than part-skim, while a store-brand tub works well here. Part-skim ricotta is a workable swap, though the finished filling is less lush and may feel a little firmer.
- Low-moisture mozzarella — This melts into the filling without releasing the extra moisture that fresh mozzarella would bring. A basic bag of shredded low-moisture mozzarella is fine; part-skim low-moisture mozzarella also works and gives a slightly less rich result. Keep the cheese divided as listed so some goes into the filling and the rest melts over the top.
- Parmesan — Grated Parmesan adds a salty, savory edge that balances the mild ricotta. Freshly grated cheese melts smoothly, but the grated kind from the refrigerator case is practical and works well. Pecorino Romano can stand in at the same amount if you like a sharper, saltier finish.
- Cremini mushrooms and baby spinach — Cremini have a deeper, earthier taste than white mushrooms, but white button mushrooms are an easy one-for-one swap by weight. Baby spinach is tender and needs no chopping; mature spinach works too if you remove tough stems and chop the leaves before cooking.
- Marinara sauce — A jarred sauce keeps assembly straightforward and gives the shells enough tomato sauce to bake in. Choose a marinara you already like, since its flavor carries through the finished dish; a store-brand jar is perfectly suitable. A smooth or chunky style both work.
- Egg — The egg helps the ricotta filling set as it bakes, so it holds its shape when you serve the shells. Use a large egg, as listed, and mix it in only after the vegetables have cooled to just warm.
How to Fill and Bake the Shells Without Losing Their Shape
Boil the shells just shy of tender
Heat the oven to 375°F while you bring water to a boil in an 8-quart pot. Add the kosher salt and jumbo shells, then cook them for 1 minute less than the package directions; they’ll soften more in the oven. Drain them carefully so the shells stay intact and easy to fill. Fully tender shells are more likely to split when you handle them.
Cook down the mushrooms and wilt the spinach
Heat the olive oil in a 12-inch skillet over medium heat, then add the finely chopped mushrooms. Cook for 7 to 9 minutes, stirring occasionally, until they’re browned and their liquid has evaporated. Stir in the minced garlic for 30 seconds, then add the spinach in handfuls. Keep stirring for about 2 to 3 minutes, just until the leaves have wilted.
Mix the filling once the vegetables are just warm
Transfer the mushroom mixture to a medium bowl and let it cool for 10 minutes, until just warm. Stir in the ricotta, egg, 1 1/2 cups of the mozzarella, 1/2 cup of the Parmesan, the salt, and pepper until evenly combined. The mixture should be thick enough to stay in the shell rather than run off a spoon. Set aside the remaining mozzarella and Parmesan for the top.
Cover, bake, and uncover for the bubbly finish
Spread 1 cup of marinara in a 9×13-inch baking dish. Fill the shells with the ricotta mixture and arrange them in the dish, then spoon the remaining sauce over the shells and sprinkle on the reserved mozzarella and Parmesan. Cover tightly with foil and bake for 25 minutes, then uncover and bake for 10 to 15 minutes more. Look for bubbling sauce, and check that the center of the filling reaches 160°F.
Let the filling settle before serving
Take the dish out of the oven and let the shells rest for 10 minutes. The filling firms slightly as it settles, so the shells are easier to lift without spilling. Serve them while the sauce is still warm and the cheese on top is melted.
Two Simple Swaps for Different Kitchens
Make the shells gluten-free
Use a 12-ounce box of gluten-free jumbo shells in place of the regular pasta. Follow the package timing and stop cooking 1 minute early, as with the original; gluten-free shells can be more delicate, so drain them gently and fill any that stay intact. The filling and sauce remain the same, but the shells may have a softer texture.
Use white button mushrooms instead
Swap the cremini for the same weight of finely chopped white button mushrooms and cook them the same way, until browned and their liquid has evaporated. They have a milder taste, so the filling will be a little less earthy, but the texture works just as well.
Storage and Reheating
- Refrigerator: Store leftovers covered for 3 to 4 days. The pasta softens a little as it sits, but the filling stays creamy.
- Freezer: Freeze cooled portions in an airtight, freezer-safe container for up to 2 months. Thaw overnight in the refrigerator for more even reheating.
- Reheating: Cover a portion and warm it in a 350°F oven until the center reaches 165°F. Keep it covered so the edges don’t dry out; reheating uncovered can toughen the pasta before the middle is hot.
Questions That Come Up When Making Stuffed Shells
Mushroom and Spinach Stuffed Shells
Ingredients
Equipment
Method
- Heat the oven to 375°F.
- Bring water to a boil in an 8-quart pot, add the 1 tablespoon kosher salt and pasta shells, and cook 1 minute less than the package directions; drain.
- Heat the olive oil in a 12-inch skillet over medium heat, add the finely chopped cremini mushrooms, and cook for 7 to 9 minutes, stirring occasionally, until browned and their liquid has evaporated.
- Stir in the minced garlic and cook for 30 seconds.
- Add the baby spinach in handfuls and stir until wilted, about 2 to 3 minutes.
- Transfer the mushroom mixture to a medium bowl and let it cool for 10 minutes, until just warm.
- Mix in the whole-milk ricotta, large egg, 1 1/2 cups of the shredded low-moisture mozzarella, 1/2 cup of the grated Parmesan, 1/2 teaspoon kosher salt, and 1/4 teaspoon black pepper.
- Spread 1 cup of the marinara sauce in a 9x13-inch baking dish.
- Fill the shells with the ricotta mixture.
- Arrange the filled shells in the dish.
- Spoon the remaining marinara sauce over the shells and sprinkle with the remaining 1/2 cup mozzarella and 1/4 cup Parmesan.
- Cover the dish tightly with foil and bake for 25 minutes.
- Uncover and bake for 10 to 15 minutes, until bubbling and the center of the filling reaches 160°F.
- Let the shells rest for 10 minutes before serving.
