Bubbling hot out of the oven, tender white fish and sliced potatoes are blanketed in a cheesy white sauce flavored with dried herbs and lemon zest, then topped with buttery crumbs and baked until golden. This is comfort food at its most comforting. Preheat the oven, build a cozy fire, and tuck into this traditional east coast Canadian dish.
Ingredients
1 ½ pounds white fish fillets, such as cod, rockfish, or halibut, thawed Available in Our Premium Subscription Box
Salt and freshly ground black pepper
1 ½ pounds medium Yukon gold potatoes, peeled and sliced ¼-inch thick
3 tablespoons unsalted butter
½ cup finely chopped yellow onion
½ teaspoon dried thyme or 2 teaspoons fresh thyme leaves
3 tablespoons all-purpose flour
2 cups whole milk or half and half (See Pro Tips)
8 ounces gruyere, cheddar, or Monterey Jack cheese, shredded
2 teaspoons Dijon mustard
½ teaspoon finely grated lemon zest
¼ cup unseasoned breadcrumbs or panko, divided
2 tablespoons freshly grated parmesan cheese
1 tablespoon extra virgin olive oil
Green salad for serving
Directions
Preheat the Oven and Prep the Fish
Preheat the oven to 375°F with racks in the center position. Lightly sprinkle the fish all over with salt and let sit while the oven preheats.
Par-boil the Potatoes
Meanwhile, bring a large saucepan of salted water to a boil. Add the potatoes and return to a boil. Cook until just tender, about 5 minutes. Drain well and pat dry. Arrange the potatoes in a large oven proof baking dish or skillet or divide them between 6 shallow individual baking dishes.
Make the Cheese Sauce
In a medium saucepan over medium-high heat, melt the butter. Add the onion, thyme, and a pinch of salt and cook, stirring occasionally, until softened, about 5 minutes. Add the flour and using a whisk, cook, whisking constantly for about 1 minute to cook off the floury taste.
Gently whisking, add the milk in a slow stream. Bring to a simmer whisking frequently, and cook until the sauce is thickened, about 5 minutes. Remove from the heat, then add the gruyere cheese, mustard, and lemon zest and whisk until the cheese is melted. Season with salt and pepper.
Assemble
Pat the fish very dry to remove excess water and cut into 1-inch chunks. Sprinkle 2 tablespoons of the breadcrumbs over the potatoes. Add the fish and spoon the sauce over top. In a small bowl combine the remaining breadcrumbs, parmesan, and oil.
Bake and Serve
Scatter the crumbs evenly over the fish and bake on the center oven rack until bubbling and golden, 35 to 40 minutes. For more toasted breadcrumbs, switch the oven to broil for a few minutes, until very golden, watching carefully as broilers vary. Serve right away with a tart green salad alongside.
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Pro Tips
Wine Suggestion
Pour a dry or off-dry white to balance the richness. Chenin blanc, gewürztraminer, pinot gris, and riesling are all great choices. Or to match the buttery richness, go for a white Burgundy or viognier.
Dairy Options
Low fat or skim milk will result in a watery casserole because they lack the fat necessary for emulsification. Whole milk or half and half, or better yet, equal parts half and half and heavy cream will yield a creamier, smoother sauce.
Change it Up
To make this an all-in-one casserole, add a layer of thawed and squeezed frozen spinach between the cod and white sauce. Or fold any type of cooked green vegetable into the sauce along with the cheese.
Leftover Magic
In a saucepan, combine any leftover gratin with a dash of milk and bottled clam juice for a quick creamy chowder. Add a slurry of cornstarch if desired for a thicker chowder.
