Sea salt and black or white pepper

2 small heads or 1 large head cauliflower (about 2 1/2 pounds), trimmed into florets and bite-size stems

3 tablespoons butter

1 large shallot, finely chopped

2 rounded tablespoons flour

1/2 cup dry white wine

1 1/2 cups whole milk

Freshly grated nutmeg

1 tablespoon dijon mustard

1 cup shredded gruyere cheese (about 4 ounces)

1/2 pound french-style ham, prosciutto cotto or rosemary ham, cut into 1/4-inch pieces

1/2 cup grated parmigiano-reggiano cheese

A generous handful flat-leaf parsley, finely chopped