Heat the oven to 375°F and lightly grease a 9-by-13-inch baking dish.

Cook the jumbo shells in well-salted boiling water until just shy of al dente, usually about 2 minutes less than the package directions. Reserve 2 to 4 tablespoons of pasta water, then drain and briefly rinse the shells with cool water.

Heat 2 tablespoons butter and the olive oil in a large skillet over medium heat. Add 4 minced garlic cloves and cook for about 30 seconds.

Add the chopped shrimp, kosher salt, black pepper, and optional red pepper flakes. Cook for 2 to 3 minutes, stirring, until the shrimp are just pink and nearly cooked through.

Add the wine or chicken broth and lemon juice. Simmer for 1 to 2 minutes, then remove the skillet from the heat.

Stir the softened cream cheese, Parmesan, mozzarella, lemon zest, and parsley into the warm shrimp mixture. Add 1 to 2 tablespoons reserved pasta water if the filling is very thick.

For the sauce, melt 2 tablespoons butter in a saucepan. Add 2 minced garlic cloves and cook for 30 seconds, then stir in the heavy cream and simmer gently for 2 to 3 minutes.

Whisk the Parmesan, optional mozzarella, and black pepper into the cream. Thin the sauce with reserved pasta water if needed.

Spread about half of the sauce over the bottom of the prepared baking dish. Fill each shell with approximately 2 tablespoons of shrimp mixture and arrange the shells snugly in the dish.

Spoon the remaining sauce over the shells, cover the dish with foil, and bake for 20 minutes. Uncover and bake for another 8 to 12 minutes, until the sauce is bubbling and the top is lightly browned.

Let the stuffed shells rest for 5 minutes before serving. Garnish with additional parsley, Parmesan, and lemon zest.