Another super recipe by Alison Roman from her book “Nothing Fancy” I recommend you buy it!
This gratin smothers thick slabs of tender cauliflower in a creamy sauce and lots of cheese. The bread crumb studding is optional, but a highly delicious addition.
1 cup heavy cream
4 tbsp unsalted butter
2 garlic cloves, finely grated
Kosher salt and freshly ground black pepper
2 1/2 –3-pound cauliflower, leafy green parts removed
1/2 small sweet or yellow onion, very thinly sliced
6 oz Gruyère or white cheddar cheese, grated (about 2 1/2 cups)
Red pepper flakes (optional)
2 cups fresh coarse bread crumbs or panko (optional)
3 tbsp white sesame seeds
1/4 cup olive oil (optional)
Preheat the oven to 425°F.
Bring the cream, butter and garlic to a simmer in a small pot over medium heat. Season with salt and pepper and remove from heat.
Slice the cauliflower into ½-inch-thick slabs (some of the bits will fall away and crumble into tiny florets; this is fine).
Place the smallest bits of cauliflower on the bottom of a 9-inch pie plate or cake pan (I like the roundness of the pie plates and cake pans, but a 2-quart baking dish of any shape will work). Scatter with some of the onion, followed by some of the cheese. Repeat with the remaining cauliflower, onion, and cheese until all of it is used, ending with the cheese.
Pour the cream mixture over (leave the garlic in or remove), followed by a good sprinkle of crushed red pepper flakes, if using.
Cover with aluminum foil and bake until the cauliflower is tender and cooked through, 25 to 30 minutes.
If using the bread crumbs: now is the time to put them to use. Combine the bread crumbs, sesame seeds, and olive oil in a medium bowl (alternatively just use sesame seeds). Season with salt and pepper.
Remove the foil and continue to bake until the top is bubbly and golden and the cream is mostly reduced, another 15 to 20 minutes (it will look slightly runny and creamy in the oven but will set and thicken once you take it out of the oven and let it cool a few minutes).
Scatter the bread crumb mixture (alternatively, just scatter the sesame seeds) over the top and bake until those are deeply and thoroughly crispy and golden brown, 8 to 10 minutes.
Remove from the oven and let cool slightly before serving.
Do-ahead tip
Gratin (sans bread crumbs) can be baked 2 days ahead, then kept covered and refrigerated. To reheat, place in a 400°F. oven, uncovered (adding bread crumbs, if using), until returned to its bubbling, golden state, 10 to 15 minutes