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Ingredients
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Potatoes & Base
Smokey Cream Sauce
Cheese & Topping
Method
Potatoes & Prep
- 1
Preheat and prepare
Preheat oven to 375°F (190°C). Lightly butter or spray a 9x13-inch baking dish (or similar) and set aside.
- 2
Slice potatoes
Peel potatoes if desired and slice them into 1/8- to 1/4-inch thick rounds using a sharp knife or mandoline for even cooking. Place slices in a large bowl of cold water to remove excess starch while you prepare other ingredients.
- 3
Prepare aromatics
Peel and thinly slice the yellow onion. Mince the garlic cloves and set both aside.
Make Smokey Cream Sauce
- 4
Sweat onion and garlic
In a medium saucepan over medium heat, melt 1 tablespoon of the butter. Add the sliced onion and a pinch (about 1/8 tsp) of salt and cook, stirring occasionally, until the onion is soft and translucent, about 6–8 minutes. Add the minced garlic and cook 30–45 seconds until fragrant.
- 5
- 6
Add liquids and seasonings
Slowly whisk in the vegetable broth (or water) until smooth, then whisk in the milk and cream. Bring the mixture to a gentle simmer while whisking to incorporate. Add the smoked paprika, liquid smoke, Dijon mustard, kosher salt, and black pepper. Continue to simmer gently for 3–4 minutes until sauce thickens to coat the back of a spoon. Taste and adjust seasoning (add more liquid smoke or smoked paprika if you want a stronger smokey note).
Assemble & Bake
- 7
Layer potatoes
Drain the potato slices and pat dry with a clean towel. Arrange about half of the potato slices in an even layer in the prepared baking dish. Sprinkle about half of the sliced onions over the potatoes and season lightly with 1/2 teaspoon of the kosher salt and a few grinds of black pepper. Sprinkle 1 cup of the grated cheddar and 1/4 cup of the Gruyère (if using) over this layer. Pour roughly half of the smokey cream sauce over the layer so potatoes are evenly moistened.
- 8
Second layer
Add the remaining potato slices in an overlapping layer, top with the remaining onions, remaining salt and pepper, and the rest of the cheeses (reserve about 1/4 cup of cheddar and a tablespoon of Parmesan for topping). Pour the remaining sauce evenly over the assembled potatoes, gently pressing down so the sauce settles between slices.
- 9
Top and bake
In a small bowl, toss panko breadcrumbs with 2 tablespoons olive oil and the remaining Parmesan cheese. Sprinkle the breadcrumb mixture evenly over the top and finish with the reserved cheddar. Cover dish tightly with aluminum foil and bake in the preheated oven for 35 minutes. Remove foil and bake uncovered for an additional 20–25 minutes until the top is golden brown and potatoes are tender when pierced with a knife. If top browns too quickly, tent with foil.
Finish & Serve
- 10
Rest and garnish
Remove the gratin from the oven and let rest for 10–15 minutes so the sauce sets slightly. Sprinkle chopped fresh parsley over the top before serving.
- 11
Serve
Cut into portions and serve warm as a vegetarian side or main. Leftovers keep covered in the refrigerator for up to 3 days; reheat covered in a 350°F (175°C) oven until warmed through.