Mashed potato au gratin

Peel russet potatoes, cut in half across the middle, stand on the flat side and halve again into quarters.

Cover by a couple inches of cold water, add a very generous amount of salt and set on high heat. Once boiling, drop to medium and cook until very tender but not falling apart, tested with a knife; overcooked potatoes absorb water and dilute the flavor.

Peel the potatoes for the top, halve lengthwise and hold covered in water.

Drain the cooked potatoes very well, return to the pot and mash fairly fine.

Add butter, salt and, if wanted, a few shakes of cayenne; mash and stir until the butter disappears and the potatoes are fairly smooth.

Stir in whole milk and a big handful of Comte. Taste and add salt if bland.

Butter a casserole dish, transfer the mash in, press it into the corners with no air pockets and smooth the top.

Season the surface with freshly ground black pepper and a generous application of salt, so the sliced potatoes sit in contact with it.

Slice the halved potatoes an eighth of an inch thick, guiding the knife with the index finger and using a forward-then-back cut; discard the first small slice or two.

Fan each sliced half and transfer it onto the mash in rows, adjusting the rows to the dish, until the surface is covered with slices fanned at a slight angle.

Salt the top generously and brush all over with melted butter until drenched.

Scatter grated Comte over, not covering completely, and finish with a grating of Parmigiano Reggiano.

Set the dish on a sheet pan to catch dripping butter and bake in the center of a 450 degree oven for about an hour to an hour 15 minutes, until the top potatoes are tender.

Rest 10 to 15 minutes before serving; it sinks a little. Sprinkle with a few chives.