Step 1

Lightly grease a rimmed baking sheet with the oil and set aside.

Step 2

Bring a large pot of salted water to a boil. Add the pasta shells and cook until al dente according to the package directions. Reserve 1 cup of the cooking water and set aside for making the Vodka Sauce. Drain the pasta and rinse under cold water to stop the cooking. Drain well. Arrange the pasta in a single layer on the prepared baking sheet.

Step 3

In a food processor, add the mushrooms and shallot and pulse until chopped into about 1/8-inch pieces. In a large skillet over medium-high heat, melt the butter. Add the mushrooms and shallots. Cook, stirring occasionally, until the mushrooms are browned, 5 to 7 minutes. Add salt and pepper to taste. Add the spinach to the skillet and cover to allow the spinach to wilt, about 2 minutes more. Stir in the parsley and transfer to a large bowl.

Step 4

In a medium bowl, combine the ricotta, pine nuts, basil chiffonade, 1 cup mozzarella, 1/4 cup Parmesan and 1/2 teaspoon salt. Combine the cheese mixture with the mushroom mixture. Stuff each shell with about 2 tablespoons of the filling.

Step 5

In the skillet where the mushrooms were cooked, add about 1 cup Vodka Sauce and spread it in an even layer. Arrange the stuffed shells in a circular pattern. Add the remaining 1 1/2 cups sauce, 1/4 cup Parmesan and 1/2 cup mozzarella in between and on top of the shells (leaving the tops of the shells mostly exposed). Cover and cook over medium heat until the cheese is melted and bubbling, about 10 minutes.

Step 6

Garnish with more Parmesan and basil leaves, and serve.

Step 7

In a large skillet over low heat, add the butter, onion, garlic and red pepper flakes. Cook, stirring occasionally, until softened, 5 to 10 minutes. Increase the heat to medium-high and add the tomatoes, cream, vodka, tomato paste, 1/2 cup pasta cooking water and salt and pepper to taste. Let simmer for about 10 minutes, adding more reserved pasta water as needed.