French Onion Potato Bake
Thin slices of russet potato bake in cream, sour cream, and dry French onion soup mix, then get a browned Gruyère topping. The finished casserole should be creamy and easy to scoop, with distinct potato slices beneath the cheese.
The key is to cook the potatoes through before adding the final layer of cheese. Bake covered until a knife slides easily through the center, then uncover to brown the top. A short rest helps the sauce settle without turning the casserole into a firm, sliceable square.
Ingredients for French Onion Potato Bake
- 1 teaspoon unsalted butter, for the dish
- 1 1/2 cups heavy cream (360g)
- 1/2 cup sour cream (120g)
- 1 packet dry French onion soup mix, about 1 ounce (28g)
- 3 pounds russet potatoes (about 1,350g), peeled and sliced about 1/8 inch thick
- 2 cups shredded Gruyère cheese (225g), divided
Soup-mix packets vary in saltiness, so do not add salt automatically.
How to Make French Onion Potato Bake
- Prepare the oven and dish: Preheat the oven to 400°F (205°C). Lightly butter a 9-by-13-inch baking dish deep enough to hold the sauce without filling it to the rim.
- Mix the onion cream: Whisk the heavy cream, sour cream, and entire soup-mix packet in a large bowl until evenly combined.
- Slice and layer: Peel and slice the potatoes about 1/8 inch thick. Work promptly so the cut potatoes do not sit exposed and discolor. Arrange half the slices in overlapping layers in the dish. Pour over half the onion cream and scatter with 1 cup Gruyère. Add the remaining potatoes and cream, coating the top slices. Reserve the last cup of cheese.
- Bake until tender: Cover securely with foil, keeping it off the potatoes where possible. If the foil must touch the surface, place parchment beneath it. Bake for about 50 to 65 minutes. Starting at 50 minutes, test the center with a thin knife. If you feel firm resistance, cover again and bake in 10-minute increments until the knife slides through easily and the sauce bubbles near the edges.
- Brown the cheese: Remove the foil and scatter the reserved Gruyère over the potatoes. Bake uncovered for about 10 to 15 minutes, checking after 8 minutes, until the cheese bubbles and develops uneven golden to deep amber-brown patches.
- Rest and serve: Let the casserole stand for 10 to 15 minutes before scooping. Portions should hold together loosely, with creamy, visible potato slices beneath the browned cheese.
Why the Center-Tenderness Test Matters
Even 1/8-inch slices help the potatoes cook at the same rate, but the center can lag behind the edges. Test the middle before adding the topping: if the potatoes are still firm after the cheese browns, more oven time could take the cheese too far. Thicker slices, a deeper dish, or a casserole baked cold from the refrigerator may need extra covered time.
Ingredient Swaps
Shredded Swiss can replace the Gruyère in the same amount. Yukon Gold potatoes also work, though the sauce may be looser; keep the center-tenderness check and resting time. For another sliced-potato bake, try Cheesy Au Gratin Potatoes with Golden Cheddar.
Serving, Make-Ahead, and Leftovers
Serve with roast chicken, pork tenderloin, or a green vegetable such as broccoli. For a different creamy potato side, see Steakhouse Potatoes Romanoff with Sharp Cheddar.
To assemble ahead, cover the unbaked casserole and refrigerate it for a few hours. If it goes into the oven cold, allow extra covered baking time and use the center-knife test to judge when it is ready for the cheese topping.
Refrigerate leftovers in an airtight container for up to 3 days. Reheat gently until hot throughout; the potatoes may be softer than when freshly baked. Freezing is possible, but thawed potatoes may soften further.
Nutrition
Approximate nutrition per serving, based on 8 side-dish servings: 450 calories, 14g protein, 29g fat, and 34g carbohydrates. Per 100g of finished casserole: approximately 190 calories, 6g protein, 12g fat, and 15g carbohydrates. Values vary with the soup mix, cheese, and moisture lost during baking.
Equipment
- 9-by-13-inch baking dish
- Large mixing bowl
- Whisk
- Aluminum foil
- Thin knife
Ingredients
For the casserole
- 1 teaspoon unsalted butter, for the dish
- 1 1/2 cups heavy cream (360g)
- 1/2 cup sour cream (120g)
- 1 packet dry French onion soup mix, about 1 ounce (28g)
- 3 pounds russet potatoes (about 1,350g), peeled and sliced about 1/8 inch thick
- 2 cups shredded Gruyère cheese (225g), divided
Instructions
- Preheat the oven to 400°F (205°C). Lightly butter a 9-by-13-inch baking dish deep enough to hold the sauce without filling it to the rim.
- Whisk the heavy cream, sour cream, and French onion soup mix together in a large bowl.
- Peel and slice the potatoes about 1/8 inch thick. Arrange half in overlapping layers in the dish.
- Pour half the onion cream over the potatoes and sprinkle with 1 cup Gruyère. Add the remaining potatoes and cream, coating the top slices. Reserve the remaining cheese.
- Cover the dish securely with foil, keeping it off the potatoes if possible. If the foil may touch the surface, place parchment beneath it.
- Bake for 50 to 65 minutes. Starting at 50 minutes, test the center with a thin knife. If the potatoes are firm, cover again and bake in 10-minute increments until the knife slides through easily and the sauce bubbles near the edges.
- Remove the foil and sprinkle the reserved Gruyère over the potatoes. Bake uncovered for 10 to 15 minutes, checking after 8 minutes, until bubbling and browned.
- Rest for 10 to 15 minutes before scooping and serving.
Tips
- Slice the potatoes evenly, about 1/8 inch thick, so they cook at a similar rate.
- Test the center for tenderness before adding the cheese topping.
- Avoid adding salt automatically because soup-mix packets vary in saltiness.
- If baking the casserole straight from the refrigerator, allow extra covered baking time and check the center with a knife.
- Rest the casserole briefly so the sauce can settle while remaining creamy.
Variations
- Swiss Cheese Potato Bake: Replace the Gruyère with the same amount of shredded Swiss cheese.
- Yukon Gold Potato Bake: Use Yukon Gold potatoes instead of russets; the sauce may be looser, so keep the center-tenderness check and resting time.