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Cheesy Potato and Sweet Onion Gratin

Prep Time20 minutes
Cook Time1 hour 50 minutes
Total Time2 hours 10 minutes
Course: Side Dish
Cuisine: French
Keyword: brie cheese, butter, fresh herbs, gluten free, Gruyére cheeses, heavy cream, olive oil, Onions, parmesan cheese, rosemary, russet potatoes, sage, thyme, white wine
Servings: 6 servings
Author: GFchow @ gfchow.com

Equipment

  • Mandolin
  • 7" x 10" or 9" x 9" Baking Dish

Ingredients

  • 4 tablespoons olive oil divided
  • 2 large sweet onions such as vidalia cut in half lengthwise through the root, sliced thinly with a mandolin or by hand
  • 1/2 cup white wine optional (wine you would drink!)
  • 2 tablespoons fresh herbs - sage, thyme, rosemary rough chopped
  • 3-4 large russet potatoes peeled, sliced into rounds using a mandolin, otherwise slice as thinly as possible by hand. See NOTES below.
  • 2 1/2 cups Gruyere and/or Swiss, shredded (Trader Joe's has a pre-packaged shredded Gruyere/Swiss mix that is amazing) or a wedge of Brie, sliced (other cheeses that melt easily can be used)
  • 4 tablespoons heavy cream divided
  • 1/4 cup parmesan cheese grated
  • Kosher salt and pepper to season the potatoes and onions
  • pat of butter salted or unsalted to grease the baking dish or cast iron pan

Instructions

  • Heat 2 tablespoons olive oil in a large pan over medium heat. Add onions, fresh herbs, and season with kosher salt and freshly ground pepper. Stir occasionally and cook until onions are caramelized, approximately 15 mins. For added flavor, add 1/2 cup white wine and cook for an additional 5 mins until the wine has evaporated, optional.
  • While onions are cooking, slice the potatoes. Cover the potatoes with a damp cloth or paper towel to keep them from browning.
  • Preheat oven to 350 degrees.
  • Once onions are cooked and potatoes are sliced, it’s time to assemble the dish. Lightly butter the baking dish. Start by placing one-third of the potato slices into the pan slightly overlapping them until bottom of dish is covered. Next, add half of the sautéed onions. Then scatter one cup of grated gruyere cheese on top or a couple of slices of Brie followed by drizzling 2 tablespoons of heavy cream. Season with kosher salt and pepper.
  • Repeat…one-third of potatoes, remainder of sautéd onions, one cup grated gruyere cheese or a couple of slices of Brie, and 2 tablespoons heavy cream.
  • Finish assembly with remaining one-third of potatoes topped with final 1/2 cup of gruyere cheese and 1/4 cup of Parmesan. (If using the Brie throughout, it will not be used in this last step.) Season with kosher salt and finish by drizzling remaining two tablespoons of olive oil on top. Cover gratin with foil.
  • Place dish on middle rack in the oven and cook for 1 hour covered. Then remove foil, raise oven temperature to 425 degrees and continue cooking uncovered for and additional 1/2 hour. Total cooking time is 1 1/2 hours.
  • Let gratin rest for 5 minutes and then serve.

Notes

Always buy a few more potatoes than you intend to use because often times one or two potatoes can have significant brown spots (similar to avocados!) and you won't know until you cut into them.
The amount of onions you choose to use is up to you. I love sautéed onions and think they add a lot to the recipe but if you’re not an onion fan, you can omit the onions altogether or cook just one onion.
When using the Brie cheese, the gratin will be creamier than if using the Gruyere. The Gruyere will result in a nuttier, cheesier taste and presentation. Try both ways!
If you have leftover gratin, the best way to reheat the potatoes is to microwave them with a wet paper towel on top which keeps the potatoes moist.