Step 1

Preheat oven to 375 degrees. Butter, oil or spray two small baking dishes large enough to hold the potatoes and the cheese sauce with cooking spray.

Step 2

Place potatoes, onion and garlic in a small saucepan. Add heavy cream and salt and white or black pepper to taste.

Step 3

Bring to a simmer and gently cook the potatoes for 5 minutes after the cream comes to a simmer, stirring carefully once or twice, being careful to not break up the potatoes.

Step 4

Remove potatoes, onions and garlic to a bowl with a slotted spoon. Let cool slightly so you can handle them.

Step 5

Whisk grated cheese into the cream until smooth, returning the cream to low heat if necessary to smooth out the cheese sauce.

Step 6

Add dry mustard, cayenne and salt and pepper to taste.

Step 7

Layer 1/3 of the potatoes into the two individual baking dishes (1/6 into each dish). Drizzle each dish with 1/3 of the cheese sauce. Repeat layering two more times, finishing with cheese sauce.

Step 8

Place on a baking sheet and cover loosely with aluminum foil. Bake for 35-40 minutes or until the potatoes are tender and the gratins are bubbling. Remove the aluminum foil 10 to 15 minutes before they're done so the cheese browns slightly.