It's important to begin with spinach leaves that are completely dry. Although the leaves cook slightly, they shouldn't release liquid or they'll dilute the dressing.Plus: More Vegetable Recipes and Tips
In a small bowl, combine the oil, vinegar, shallots, pepper and 3/4 teaspoon of salt. Set a large enameled cast-iron casserole over high heat. When very hot, add the vinaigrette and bring to a boil. Add the spinach in large handfuls, tossing constantly with tongs until the leaves are partially wilted before adding the next batch. When most of the spinach is wilted, after about 4 minutes, remove the casserole from the heat. Season the spinach with salt, transfer to a bowl and serve at once.