Step 1

Preheat the oven to 375 with racks in the middle and upper third of the oven. Bring a large Dutch oven or stockpot of water to boil over high heat. Generously salt the water (use at least 2 teaspoons). If you’re not using frozen greens, fill a large bowl with ice water for blanching.

Step 2

If you’re using fresh greens, add them to the boiling water and cook just until wilted, about 20 to 40 seconds. Using tongs (leave the water in the pot), transfer the greens to the ice bath and let them cool down. Drain off the water and squeeze as much excess water from the greens as possible. Set aside. (If you’re using frozen greens, place them in a colander and run cool water over them until they’ve full defrosted. Squeeze out as much excess water as possible, and set aside.)

Step 3

Bring the water in the pot back to a boil. Gently add the pasta shells in handfuls so they don’t break on the way in. Cook until pliable but just shy of al dente, about 10 minutes, stirring often so they don’t stick to the pot. Drain off the water, return the noodles to the pot, and gently stir in the olive oil to prevent the noodles from sticking. Set aside.

Step 4

Turn on your food processor and drop the garlic through the feeding tube. Once the garlic is chopped and stuck to the sides of the bowl, stop the machine and scrape down the sides. For good measure, squeeze off any remaining water in the greens, then add them to the bowl. Process until the greens are chopped into small pieces.

Step 5

Add the ricotta and process until well blended. Add half of the mozzarella, reserving the rest for topping. Add all of the Parmesan and chives, about 10 twists of black pepper, the red pepper flakes and salt. Blend well. Taste, and add additional salt, pepper or red pepper flakes if desired. Finally, add the egg and process until blended. Set aside.

Step 6

If you have an extra-large baking dish (larger than 9×13 inches), spread 1 cup of the marinara sauce across the bottom. Otherwise, divide 1 cup marinara between a large (9×13 inches) and medium-sized baker (say, an 8-inch square). You might need to add another splash of sauce to evenly coat the bottom of the pans.

Step 7

Stuff each intact shell with a heaping spoonful (about 1 ½ to 2 tablespoons) of the green mixture. Place each stuffed shell in the baker in rows. (You might have a few leftover or broken shells; save them for another use.) Spoon the remaining marinara sauce over the tops of the shells. Top the shells with the remaining mozzarella.

Step 8

Cover the baker(s) tightly with foil and bake on the middle rack for 30 minutes. Then, remove the foil and place the bakers on the upper rack. Bake for 5 to 10 more minutes, until the mozzarella is fully melted and turning just slightly golden (you can bake longer for a more golden effect, but the greens will become less vibrant).

Step 9

Garnish the shells with a light dusting of grated Parmesan and some small or torn fresh basil leaves. Leftover shells will keep well in the refrigerator for up to 4 days, or freeze them for several months.