GRANNY'S HAM AND POTATO GRATIN FOR A CROWD

Steps:

• THE POTATOES: Have ready the kettle containing 4 cups of cold water.
• Peel the potatoes and slice them 1/4 inch thick, dropping them into the cold water to cover as you do so. Cover the kettle, and bring to the boil.
• Uncover and boil slowly for 3 to 4 minutes, until barely cooked through and eat several slices to check.
• Drain, cover the kettle again for 3 to 4 minutes to firm up the potato slices, then uncover.
• THE GARLIC AND MUSTARD SAUCE: Make the classic white sauce; cook the butter and flour together in the saucepan until they foam and froth for 2 minutes without coloring.
• Turn off heat and pour in half the hot milk.
• Whisk vigorously to blend as you pour in the rest.
• Simmer for 3 minutes, stirring.
• Remove from heat and whisk in the seasonings.
• Bring to the simmer again.
• Taste carefully, and add additional seasonings to taste.
• ASSEMBLING: Spoon a 1/16-inch layer of sauce on the bottom of the buttered baking dish.
• Set aside 3 cups of the sauce and 1 cup of the cheese for the topping.
• (Swiss or a mixture such as swiss, mozzarella, jack, and/or cheddar.)
• Now, to arrange everything in 4 layers, start with a quart of the potatoes, then a quarter of the ham, follow by a third of the sauce and sprinkle on a third of the cheese.
• Continue in layers, finishing the final layer with the remaining potatoes and ham.
• Spread on the reserved 3 cups of sauce to cover completely, then the last of the cheese.
• AHEAD OF TIME NOTE: May be kept warm uncovered on a hot tray but be sure not to overheat or the potatoes and ham will dry out.