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French Onion Potato Bake

French onion potato bake with thinly sliced Yukon gold potatoes layered under deeply caramelized onions and a beefy broth, then finished with bubbly, golden Gruyere. Low-and-slow onion cooking and a flour-thickened broth create a creamy, savory soak for tender slices.
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Prep Time 1 hour 45 minutes
Cook Time 1 hour 5 minutes
Total Time 2 hours 50 minutes
Servings: 6 servings
Course: Side Dish
Cuisine: French
Calories: 320
Ingredients Equipment Method Notes

Ingredients
  

Potatoes
  • 3 lb Yukon gold potatoes Thinly sliced for even cooking.
Onions and aromatics
  • 4 yellow onions Thinly sliced.
  • 1 tsp fresh thyme leaves Use fresh for best flavor.
Butter and thickener
  • 3 tbsp butter For cooking the onions and building the base.
  • 2 tbsp all-purpose flour Helps thicken the onion broth.
Broth and cheese
  • 2 cup beef broth For the onion sauce.
  • 2 cup shredded Gruyere cheese For topping; use a good melting quality.
Seasoning
  • salt and pepper To taste; season the potato layers.

Equipment

  • 1 cast iron skillet
  • 1 sheet pan

Method
 

Caramelize the onions
  1. Melt the butter in a skillet and cook the onions low and slow until deeply caramelized, about 30 minutes.
  2. Keep the heat low and stir as needed so the onions turn golden brown without burning, about 30 minutes total.
Thicken the onion broth
  1. Stir the flour into the caramelized onions and cook for 1 minute.
  2. Whisk in the beef broth and cook until thickened, using steady stirring until the mixture coats the back of a spoon.
Assemble the bake
  1. Layer the potato slices in a greased baking dish, seasoning each layer with salt, pepper, and thyme.
  2. Pour the onion broth mixture evenly over the potatoes so the layers settle and are mostly covered.
Bake and finish
  1. Cover with foil and bake at 375°F for 45 minutes, until the potatoes are nearly tender when pierced with a fork.
  2. Uncover, top with Gruyere, and bake at 375°F for 20 more minutes until bubbly and golden.

Notes

Slice potatoes uniformly thin with a mandoline for even cooking and fewer crunchy edges. Refrigerate leftovers in a covered container up to 4 days; reheat in a 350°F oven until warmed through. Freezing isn’t recommended because potatoes can become grainy after thawing. For a lower-fat option, use reduced-fat Gruyere and swap in part-skim dairy-based cheese (flavor will be slightly milder but still creamy).