Cheese Au Gratins Recipe

Parboil cauliflower and wilt spinach

If using cauliflower, bring a pot of salted water to a boil. Add florets and cook 3 minutes until slightly tender but not falling apart. Drain and shock in ice water to stop cooking; drain well. For spinach, sauté in a dry skillet just until wilted, then transfer to a sieve and press out excess moisture. Set both aside.

Slice potatoes

Preheat oven to 375°F (190°C). If using potatoes, wash and peel (optional). Using a mandoline or sharp knife, slice potatoes very thin (about 1/8 inch). Place slices in a bowl of cold water to remove surface starch, then drain and pat dry. Toss with 1 tsp salt.

Make a roux

In a medium saucepan over medium heat, melt 4 tbs unsalted butter. When foaming subsides, add 4 tbs all-purpose flour and whisk continuously for 1.5–2 minutes until the raw flour smell is gone and the mixture is a pale golden color, but do not let it brown.

Add milk and cream

Gradually pour in 3 cups whole milk and 1 cup heavy cream in a thin stream while whisking constantly to avoid lumps. Bring mixture to a gentle simmer (do not boil) and cook 4–6 minutes until thickened to coat the back of a spoon.

Season and finish sauce

Stir in 1 tsp Dijon mustard, 0.25 tsp cayenne, 1 tsp salt and 0.5 tsp freshly ground black pepper. Reduce heat to low. Remove about 1/2 cup of the hot sauce into a small bowl and slowly whisk it into the grated cheeses (this tempers the cheese and prevents clumping). Then add the cheese mixture back into the sauce a handful at a time, stirring until smooth and fully melted. Keep sauce warm but do not overheat or it may seize.

Butter a 9x13-inch baking dish (or individual ramekins).

Layer vegetables

If using potatoes as the main base: arrange a single even layer of potato slices across the bottom. Spoon a thin layer of cheese sauce over the potatoes to moisten. Add a second layer of potatoes, then a layer of cauliflower and/or spinach if using, then more sauce. Repeat so you finish with a layer of potatoes or vegetables topped with sauce. If not using potatoes, place cauliflower florets and wilted spinach in an even layer and pour cheese sauce over them, ensuring everything is evenly coated. Use all sauce across the dish.

Top with cheese and crumbs

In a small bowl, mix 0.75 cups breadcrumbs with 2 tbs melted butter, 2 tbs grated Parmesan and 1 tbs fresh thyme leaves (if using). Sprinkle remaining 0.25 cup grated cheddar/Gruyère mix (if any reserved) over the assembled gratin, then evenly sprinkle the breadcrumb mixture on top to create a crisp crust.

Cover the dish loosely with foil and bake in the preheated 375°F (190°C) oven for 25 minutes to heat through and allow potatoes to soften (if used). Remove foil and continue to bake 15–20 minutes more until the top is bubbling and golden brown. If top is browning too quickly, re-cover with foil.

For extra color, place under a hot broiler for 1–2 minutes watching carefully until nicely browned, then remove.

Let the gratin rest 10 minutes before serving to set. Garnish with extra thyme leaves and an additional sprinkle of Parmesan if desired.