Simplified cauliflower gratin

1 cauliflower, cut in pieces
1 cup heavy cream
1 tablespoon flour  (paleo flour if going keto)
1 cup grated Parmigiano Reggiano, or more
2/3 cup panko or bread crumbs (optional if going keto)
1 tablespoon butter, cut in small pieces
Salt, pepper to taste

Preheat oven to 390F (200C)
In a big bowl, mix the cauliflower, cream, flour and 3/4 of the parmesan; 
Add salt and pepper
Transfer to gratin dish, and cover airtight with aluminium foil
Bake 30 minutes
In a bowl, mix the rest or the parmesan and the bread crumbs.
Remove the foil, spread the mixed cheese and bread evenly, add the pieces of butter
Continue baking uncovered until the gratin is golden and cauliflower tender, 10 to 15 minutes
For a more intense color, finish with 3-5 minutes on high broil
Let rest 5 minutes before serving.

Can be made ahead and refrigerated; reheat in oven at 300F