Potatoes au Gratin - French Onion Soup Style
French Onion soup is such a labor of love that is so great at warming you up from the inside out. The creamy caramelized onions with the gooey funky cheese is an unmatched combination! But when it comes to hosting a crowd, it can be tricky to collect enough oven safe crocks to get everyones french onion under the broiler and ready to serve. This year we've combined two favorites - French Onion Soup meets Potatoes au Gratin. This dish was so decadent and is an easy side to make ahead.
- 2 tablespoons olive oil
- 4 cups yellow onions, sliced
- 4-5 large russet potatoes (about 3 pounds)
- 6 cloves garlic, sliced
- 3 cups heavy cream
- 2 tablespoons butter
- 3 teaspoons porcini powder
- 2 teaspoons dried sage
- 2 teaspoons dried thyme
- 2 sprigs fresh rosemary, chopped (or 2 teaspoons dried)
- 1 teaspoon greek oregano
- 1 tablespoon salt
- 6 ounces Gruyere Cheese
- 1 cup shredded Parmesan/Mozzarella mix
- Using a mandolin (or carefully with a sharp knife and a cutting board), slice your onions and your potatoes thinly.
- Add sliced potatoes to a large bowl with cool water.
- In a medium saute pan, heat over medium-high heat and add olive oil once preheated. Add sliced onions, and begin cooking.
- Onions will take about 40 minutes to properly caramelize, be sure to stir occasionally.
- In a small pot, melt butter over medium heat. Add garlic and cook until lightly toasted. Next, add your porcini powder, sage, thyme, rosemary and cook until fragrant. Add heavy cream and salt to pot, bring to a simmer. Set aside.
- Once your onions are done caramelizing, remove from heat to cool slightly.
- Preheat oven to 400 degrees F.
- Drain potatoes. Shred Cheeses.
- In an oven safe baking dish (roughly 8x11), begin layering 1/3 of your potatoes. Top with 1/2 your caramelized onions in an even layer and 1/3 of your cheese.
- Next, add another layer of potatoes, the rest of your onions, and another 1/3 of your cheese.
- Finally, add your final layer of potatoes and pour over your cream mixture. Top with remainder of your cheese.
- Tightly cover baking dish with aluminum foil and bake for 50 minutes. Remove foil and bake for another 10-15 minutes or until golden brown across.
- Let cool slightly before serving. To serve- cut portions with a sharp knife, sawing through all the layers. Enjoy!
If you're making this ahead, pull baking tray from oven at the 50 minute mark. Allow to cool for an hour at room temperature before chilling in fridge. When you're ready to serve, take tray out of fridge 1-2 hours before baking again at 400 degrees for 30 minutes or until golden brown and bubbling.