This classic New Orleans dish, circa 1899, gets a fresh spin with tarragon and shallots replacing the usual parsley and garlic. It gets its New England accent from a topping of buttery Ritz cracker crumbs (whose predecessor was invented in Newburyport, Massachusetts). To save time, ask your fishmonger to shuck the oysters, but be sure to save their precious liquor (juices).
Preheat oven to 425°. Line a baking sheet with an extra-long piece of aluminum foil; then bunch the foil up in spots to create 20 small wells, which will hold the oysters and keep them upright.
Make the topping: In a medium-size bowl, stir together crushed crackers and 4 tablespoons melted butter. Set aside.
In a medium-size saucepan over medium-high heat, melt 2 tablespoons butter. Add shallots and cook until translucent, about 4 minutes. Remove pan from heat and add Pernod. Return pan to heat and bring liquid to a simmer. Once simmering, remove pan from heat again and use a match to ignite the liquid, letting the alcohol burn off for 10 to 15 seconds (the flames will subside on their own).
Add cream and tarragon, bring to a simmer, and cook until reduced by half, about 10 minutes. Add spinach and cook, stirring, until wilted. Remove pan from heat, stir in cheese, and let stand until cool.
Meanwhile, shuck oysters, preserving their liquor (juices) in the shells. Nestle shells in foil on prepared baking sheet. Add 1 tablespoon sauce to each oyster and sprinkle with 1 tablespoon cracker mixture.
Bake until sauce is bubbling and topping is golden brown, about 5 minutes. Season with salt and pepper to taste.