Fusing two delicious foods into one isn’t always a winning idea (a doughnut is not a hamburger bun!), but sometimes it’s a sure thing. That’s precisely the case with this French Onion Potato Gratin.
What’s not to love about layers of potatoes braised in an intensely savory beef broth studded with sweet caramelized onions? To echo the beloved French onion soup topping of a broiled cheesy crouton, we top the potatoes with nutty Gruyère and crispy panko bread crumbs.
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To make the dish, cook sliced onions in a covered pot with butter and a little water for about 15 minutes. The steam causes the onions to break down quickly, releasing their liquid and sugars. Then, uncover the pot to cook off the liquid and continue cooking the onions. Fifteen minutes later, pull the sweet, browned onions off the heat and stir in savory beef broth, complex aromatic sherry, Dijon mustard for bite, and Worcestershire sauce for even more umami.
Next, toss in 4 pounds of sliced Yukon Gold potatoes; transfer the mixture to a baking dish; cover with foil; and bake until the potatoes are tender, uncovering them halfway through baking to allow the broth to cook down until full-bodied and superflavorful.
Finally, top the potatoes with a mixture of shredded Gruyère, panko, and fresh thyme and then return the dish to the oven until bubbling and golden.
Your reward is a delightful amalgamation of two beloved comfort foods, an irresistible cheesy topping blanketing a luscious mixture of soft potatoes, rich broth, and caramelized onions.