Inspired by the classic flavor of French onion soup, this French onion mac and cheese features deeply caramelized onions, melty Gruyere, and golden panko for a classic comfort food mash up.
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French onion mac and cheese has a depth and deliciousness inspired by classic French onion soup. The savory sweet flavor of caramelized onions suffuses the Gruyere cheese sauce. A hint of Worcestershire sauce lends an umami depth tha4t echoes the rich beef broth featured in the classic soup. And it’s all topped off with buttery panko that turns golden and crispy in the oven.
With Valentine’s Day falling squarely mid-week this year, I thought a cheesy casserole inspired by French cooking might be just the thing. And while this French onion mac and cheese is incredibly tasty, it takes a little work and time to come together. There are a few options, for dividing up the steps, though. You can caramelize the onions ahead of time. You can also prep the mac, refrigerate, and bake it a couple days later.
Some recipes will have you believe that onions can be caramelized in a half hour, but this just isn’t the case. For the richest, most developed flavor, I like to take the low and slow approach. Over low heat, the onions need minimal attention and stirring as they cook.
If you’d like the shave off some time, consider edging the heat to medium, stirring frequently, and adding drizzles of water to prevent the onions from burning or getting too brown. This guide to caramelizing onions is incredibly helpful, especially if you’re new to the technique.
Infusing the Roux with Flavor
For this French onion mac and cheese, the roux is made in the same pan used to caramelize the onions. This helps develop even more flavor in the onions and ensures the cheese sauce is imbued with caramelized onion flavor. I made my onions and roux in a 10-inch cast iron skillet, but honestly, this was a little too much liquid for the skillet. If you have a wide, deep pot or pan, use that for the onions and roux.
Bake It Up
The mac doesn’t need long in the oven – just enough time for the cheese sauce to get nice and bubbly with brown, crispy edges, and for the panko to toast to a deep golden hue.
- 5 tablespoons unsalted butter divided
- 3 large or 4 small yellow onions, trimmed, halved, and cut into paper thin half moons
- 1 teaspoon Diamond Crystal kosher salt (halve if using another kind of salt), divided
- 1/2 teaspoon freshly cracked black pepper
- 4 sprigs thyme, plus more for garnish
- 2 bay leaves, fresh or dried
- 1/4 cup all-purpose flour
- 4 cups whole milk, warmed
- 2 tablespoons Worcestershire sauce (optional)
- 16 ounces grated Gruyere
- 8 ounces grated cheddar
- 1 pound rigatoni, cavatappi, or large shell pasta, cooked 2 minutes less than recommended cook time
- 1 cup panko breadcrumbs
Set a large, wide, deep-sided skillet or pot over medium heat. Melt 2 tablespoons butter and add the onions. Cover the skillet or pot (use foil, if needed), and cook for 5 minutes. Uncover, turn heat to medium-low, and add 1/2 teaspoon each salt and pepper, 4 sprigs thyme, and bay leaves. Cook, stirring frequently, for 40 - 60 minutes, or until onions are a deep caramel hue and sweet-tasting. Onions can be caramelized ahead and kept in the fridge until needed.
While onions cook, preheat oven to 425 degrees F. Butter a 9 x 13-inch baking dish.
Once the onions have caramelized, remove thyme sprigs and bay leaves. Turn heat up to medium, add 2 tablespoons butter and 1/2 teaspoon salt. Sprinkle flour over the onions and cook, stirring constantly for 2 minutes. Stirring often, gradually add the milk in half cup increments, bringing roux to a gentle simmer between additions. Keep adding milk and stirring until mixture has thickened, about 25 minutes.
Meanwhile, cook pasta, drain, and tip into prepared baking dish.
Remove skillet or pot from heat and fold grated cheese into the roux (reserve 1/4 cup grated cheese for topping). Pour cheese mixture over the pasta and gently toss.
In a small bowl, combine the remaining tablespoon of butter with the panko and cheese. Smush the butter into the panko with your fingertips. Add a pinch each salt and pepper. Sprinkle panko mixture over top of the mac.
Mac can be prepped up to this point, covered and refrigerated for 3 days. Give it 30 minutes to come to room temp before baking.
Slide mac and cheese into the oven and bake until top is golden and filling is very bubbly, about 25 minutes. If desired garnish with thyme sprigs or leaves.