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4.67 from 3 votes

Green Bean Gratin

Tender green beans, a velvety cheese sauce, and a crisp lid of buttery breadcrumbs.
Prep Time10 mins
Cook Time25 mins
Course: Main Course, Side Dish
Cuisine: French
Keyword: casserole, easy, green beans
Servings: 6


  • 1 lb green beans, trimmed and quartered (see note below)
  • Optional: 6-8 ounces cubed ham
  • 2 cups whole milk
  • 1/4 teaspoon nutmeg
  • A generous pinch of salt plus grinds of black pepper
  • 1/2 teaspoon (or more, to taste) garlic powder
  • 1/2 teaspoon (or more, to taste) onion powder
  • 1/4 teaspoon red pepper flakes
  • 1 heaping tablespoon cornstarch blended with just enough water to make a smooth slurry
  • 6 ounces (2 cups) shredded Swiss cheese
  • Breadcrumbs from 3 slices fresh white bread
  • 3 tablespoons butter, cut into thin slices


  • Put the cut beans and 2 tablespoons of water in a bowl. Cover with plastic wrap and microwave on "high" until the beans are tender to the tooth -- 3-5 minutes. (Canned green beans will not require this preliminary heating.) Drain the beans and then transfer them and the (optional) cubed ham to a 2-quart baking dish.
  • Tip the milk into a medium-size sauce pan over medium heat. Stir in the salt, pepper, garlic powder, onion powder, and red chili flakes. When the milk begins to bubble, add the cornstarch slurry. Stir slowly and continuously until the sauce boils and thickens -- 30 seconds to 1 minute. Off heat, add the Swiss cheese. Stir until the cheese melts -- about 30 seconds.
  • Pour the cheese sauce over the beans and ham, and then stir to combine. Top with the breadcrumbs and dot with the butter.
  • Make-ahead note: The gratin can be assembled to this point. Let it come to room temperature, then cover and refrigerate for up to 24 hours.
  • Baking -- 25-30 minutes in a preheated 325°F oven. Bake until the cheese sauce begins to bubble at the sides of the dish, and the breadcrumbs brown -- 25-30 minutes. If the top has not browned appreciably after 30 minutes, place the dish 6 inches beneath the broiler. Watch carefully so that the top doesn't burn!


Fresh or frozen French fillet green beans (haricot verts) work well for this recipe, as do young, tender bush and pole beans. Avoid woody or fibrous beans -- they will not soften no matter how long you cook them.