Instructions

1. Arrange a rack in the middle of the oven and heat the oven to 400°F.
2. Bring a large pot of salted water to a boil. Add 6 ounces jumbo shells (about 22) and cook until al dente, 9 to 10 minutes. Meanwhile, trim and thinly slice 4 scallions, keeping the dark green parts separate from the whites. Finely chop 4 garlic cloves. Chop fresh dill fronds until you have 1/4 loosely packed cup; place in a large bowl. Finely grate the zest of 1 large lemon and add 1 tablespoon zest to the bowl (reserve any remaining zest for garnish). Cut the lemon in half and squeeze 2 tablespoons juice into the bowl. Stir to combine.
3. When the pasta is ready, drain and drizzle with 1 tablespoon of the olive oil. Toss to coat and set aside. If using frozen spinach, place 5 ounces in a microwave-safe bowl and microwave in 1-minute bursts until defrosted. When cool enough to handle, squeeze all the excess moisture from the spinach.
4. Heat 2 tablespoons of the olive oil in a 10-inch cast iron or other oven-safe skillet over medium heat until shimmering. Add the scallion whites and cook until softened, 2 to 3 minutes. Add the garlic and 1 cup peas. Add 5 ounces baby spinach (about 5 cups) a few handfuls at a time, until wilted, 4 to 5 minutes. If using frozen spinach, add and cook until warmed through. Remove from heat and season with 1/4 teaspoon of the kosher salt.
5. Add 1 cup ricotta, 1 cup feta (crumbling it as you add it), 2 ounces Parmesan cheese, 1 large egg, 1/4 teaspoon red pepper flakes, the remaining 1 1/4 teaspoons kosher salt, and several grinds black pepper to the bowl with the dill. Stir to combine. Add the cooked vegetables and stir to combine.
6. Wipe out the skillet and drizzle with 1 tablespoon of the olive oil, swirling the pan to coat. Stuff each shell with about 1 1/2 tablespoons of the cheese mixture and place filling-side up in the skillet. Cover the skillet with aluminum foil.
7. Bake until the filling is warmed through, about 15 minutes. Uncover and pour 1/2 cup heavy cream over the shells. Continue baking uncovered until the shells are cooked through and the cream is bubbling, 10 to 15 minutes more. Meanwhile, make the topping if desired.
8. Heat the remaining 1 tablespoon olive oil in a small skillet over medium heat until shimmering. Add 2 tablespoons pine nuts and a pinch each salt and red pepper flakes. Cook until the pine nuts are lightly golden-brown, 3 to 4 minutes. Remove from the heat.
9. When the pasta is ready, top with reserved scallion greens, lemon zest, and red pepper flakes. Spoon the pine nuts and their oil over top. Let rest 5 minutes before serving.