What's the difference between a recipe for classic Italian-American manicotti and one for stuffed shells? In all honesty, not much beyond the pasta shapes. Both have a seasoned ricotta-cheese filling, which often has spinach mixed in, and both are baked with tomato sauce and mozzarella cheese.
What does that mean in terms of coming up with a really great recipe for stuffed shells? Well, basically, that I could crib heavily from Kenji's existing manicotti recipe. As they say, there's no need to reinvent the wheel, even if the wheel in question is more of a tube filled with cheese.
We have a couple goals here: The first is building flavor, and the second is controlling moisture, which is always a risk with fresh cheese like ricotta and a water-laden vegetable like spinach. If, at the same time, we can eliminate needlessly complicated steps or superfluous ingredients, that's a bonus.
Almost all of those goals concern the filling itself, so let's start there.
One of the most important elements of this recipe is good-quality ricotta. Unfortunately, most of the ricotta sold in supermarkets is not good. It tends to have an overly grainy texture and lacks the fresh flavor of higher quality stuff. If you've got a local Italian grocer who makes or sells fresh ricotta, start there. If not, look for Calabro, our favorite nationally-available brand. If neither is an option, check the ingredients labels. You want a ricotta that has nothing more than milk, salt, and either an acid or bacterial starter. Avoid anything with a gum listed—these gums bind water but release it as you heat the ricotta up.
Straight out of its container, even good-quality ricotta can be too wet, which will result in a watery filling later. To fix this, we start by spreading the ricotta on paper towels or a clean kitchen towel on a rimmed baking sheet, then top with more towels and let it stand for about five minutes. Then we transfer the ricotta to a mixing bowl.
Next, we prep the greens. Traditionally, that would be spinach, but Kenji made a very good point when he was working on his manicotti recipe: Blanched spinach doesn't have much flavor. His solution was to use a mix of spinach and a more flavorful green like arugula, so that's what we'll be doing here, too. Arugula can be pretty peppery, but once boiled it loses a lot of its bite, so don't worry about that being a problem.
We also need to dry the boiled greens, and the fastest way to do that is to strain them directly into the strainer of a salad spinner and then spin them in it. While that removes a lot of liquid, it's not quite enough, so after that we also spread the arugula out on clean towels, roll it all up and squeeze tightly to extract as much liquid as possible. (Give yourself a forearm workout here; you won't regret it later when you cut into those shells and they're not watery.) Then, chop up the greens and add them to the ricotta.
Beyond that, we mix a few more ingredients into the filling for more flavor, like minced garlic, freshly grated nutmeg, some grated Parmigiano-Reggiano cheese, shredded mozzarella, salt, and pepper. Some recipes add mascarpone and/or an egg to the mix, but I tested both and my blind tasters couldn't tell any of the samples apart, so I concluded they weren't essential. Why add ingredients if they don't make a noticeable difference?
For the pasta, we're using jumbo shells. They're almost exclusively used for baked pasta dishes, so many of them have specific cooking instructions for baked applications. If the brand you bought doesn't have those instructions, just cut the box's recommended cooking time by three minutes—the pasta will continue to cook as it bakes.
Stuffing shells is much easier than piping cheese into manicotti. You should easily be able to fill them with a regular spoon. When filled, arrange them in a baking dish in which you've spread a thin layer of tomato sauce on the bottom. You can use whatever good tomato sauce you'd like, whether it's Kenji's slow-cooked sauce, my quick sauce, or a high quality brand like Rao's.
I like to arrange the shells with the stuffing side up. Not only does this keep them neater as they bake, it also exposes more bare pasta edges for crisping, and what's baked pasta without crisp edges? When the shells are packed in, just spoon more tomato sauce over them and top it all off with additional shredded mozzarella and grated Parmigiano-Reggiano cheese.
Home (cheese) stretch here: Bake the assembled pasta in a preheated 375°F (200°C) oven until it's browned and bubbling on top, then serve straight away.
Do you think your guests are gonna notice that you've essentially served them manicotti in a different form? We shell see.