Step 1

Bring a large pot of water to a boil and salt generously. Fill a bowl with ice water. Blanch the spinach for no more than 20 seconds, just until wilted, and transfer to the ice water, then drain. Squeeze out excess water. Bring the water in the pot back to a boil and add the pasta shells. Cook al dente, about 10 minutes, and drain and toss with the olive oil. Set aside.

Step 2

Turn on a food processor fitted with the steel blade and drop in the garlic. When the garlic is chopped and adhering to the sides of the bowl, stop the machine and scrape down the sides of the bowl. Add the spinach and pulse to chop finely. Add the ricotta and the egg and process until well blended. Add 1/3 cup of the Parmesan, the chives, and salt and pepper to taste. Pulse until well blended.

Step 3

Preheat the oven to 350 degrees. Oil a large baking dish or two 2-quart dishes. The shells should fit into the dish in one layer. Fill each shell with a scant tablespoon of the filling. Arrange in a single layer in the baking dish. Top with the tomato sauce and cover the dish with foil.

Step 4

Bake 30 minutes in the preheated oven. Remove from the heat, sprinkle on the remaining Parmesan, and serve.