Holiday ham and potato casserole

Sauté onions in butter with a big pinch of salt over medium heat a few minutes until just translucent.

Stir in flour and cook, stirring, about two minutes to take off the raw starchy edge.

Whisk in cold heavy cream, then cold milk; hot roux and cold liquid give no lumps.

Raise to medium-high and cook, stirring occasionally, until it simmers and thickens; season with more salt, black pepper, a few shakes of cayenne and grated fresh nutmeg.

Turn off the heat and whisk in a dash of Worcestershire sauce and fresh thyme leaves; set aside.

Slice the potatoes about an eighth of an inch thick on a mandolin, about three per layer, keeping them in cold water so they do not discolour.

Cover the bottom of a large deep casserole dish with about a quarter of the sauce or slightly less.

Shingle a layer of thoroughly drained potatoes, salt generously, and drip over about a third of the remaining sauce without spreading.

Add a generous layer of grated cheese and about half a pound of thinly sliced ham, pressing each layer lightly.

Repeat: potatoes, salt, a little less than half the remaining sauce, cheese, ham.

Finish with the last layer of potatoes, all the remaining sauce scraped out with a spatula, and the last of the cheese.

Bake in the center of a 350 degree oven about an hour and a half, until browned and bubbling and a knife slides into the potatoes with no effort.

Rest 15 to 20 minutes before cutting.