French Onion Soup Potato Gratin Recipe

French Onion Soup Potato Gratin Recipe

Recipe provided by The Kitchen

• Difficulty: Intermediate
• Servings: 8 to 10 portions
• Total time: 2 hours 25 minutes
• Prep time: 45 minutes

Nutritional Information Per Serving (Serving Size: 1 of 10 servings)

• Calories: 667
• Total Fat: 42 g
• Saturated Fat: 25 g
• Carbohydrates: 47 g
• Dietary Fiber: 6 g
• Sugars: 6 g
• Protein: 26 g
• Cholesterol: 126 mg
• Sodium: 924 mg

Ingredients

Caramelized Onions:

• 8 tablespoons unsalted butter (reserve wrapper)
• 5 large Spanish onions, sliced about 1/4 inch thick
• Kosher salt and freshly ground black pepper
• About 3/4 cup beef broth
• 2 tablespoons sherry
• 2 teaspoons Dijon mustard

Potato Gratin:

• 3 pounds Yukon Gold potatoes
• Kosher salt and freshly ground black pepper
• 1 pound Gruyre cheese, shredded
• 8 ounces mozzarella, shredded
• 1 1/4 cups heavy cream
• 1 1/4 cups beef broth
• One 4 1/2-ounce bag of premade croutons, lightly crushed
• One 3 1/2-ounce bag of French fried onions

Special equipment: a mandoline (optional)

Steps

1. To prepare the caramelized onions: In a large saucepan over medium-high heat, melt the butter. Once it's melted and bubbling, add a generous handful of the onions and cook until they become translucent, about 1 to 2 minutes. Continue adding onions in batches until all are in the pan. Season with a pinch of salt and pepper. Lower the heat to low and cook, stirring occasionally, until the onions develop a medium-brown color, approximately 30 minutes. If onions begin to darken too quickly, add 1 to 2 tablespoons of beef broth as needed. Stir in the sherry to deglaze the pan. Add the Dijon mustard and mix to coat the onions evenly. Season with additional salt and pepper if necessary. Remove from heat and set aside.
2. For the potato gratin: Preheat your oven to 400F.
3. Slice the potatoes thinly using a mandoline or a sharp knife, trying to keep the slices stacked for easier layering in the pan. Set aside.
4. Use the reserved butter wrapper to lightly grease the bottom and sides of a large (12-inch) cast-iron skillet, then discard the wrapper.
5. Arrange a single thin, overlapping layer of the potato slices in concentric circles along the skillet's bottom. Season with salt and pepper. Spread an even layer of caramelized onions over the potatoes. Season with salt and pepper again.
6. In a medium bowl, combine the Gruyre and mozzarella cheeses and reserve half for the topping later. Scatter a layer of the remaining cheese mix evenly over the onion layer. Repeat layering with the potatoes, onions, and cheeses until all are used (except the reserved cheese for topping). Press down firmly to compact the layers.
7. In a large measuring cup or bowl, mix the heavy cream and beef broth together and pour the mixture evenly over the gratin layers. Cover the skillet tightly with foil and place it on a baking sheet. Bake for 1 hour 15 minutes to 1 hour 30 minutes until the edges and top start browning and the potatoes are tender. Check doneness by inserting a knife into the potatoes; if it slides in easily, they are ready.
8. Remove the foil from the skillet and switch your oven broiler to high. Combine the crushed croutons with the French fried onions. Sprinkle this mixture over the gratin, then add the reserved cheeses on top. Broil the dish for 5 to 8 minutes until the topping is golden and bubbly. Serve hot and enjoy!

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