Step #1 Adjust oven rack to center position & heat oven to 350 degrees.
Step #2 Rub bottom & sides of shallow baking dish with garlic.
Step #3 Mince remaining garlic & set aside.
Step #4 Once garlic in dish has dried, about 2 mins, spread dish with half the butter.
Step #5 Bring half-and-half, potatoes, cayenne , & reserved garlic to boil in medium saucepan over medium-high heat, nutmeg, salt, stirring every once in awhile with wooden spoon Reduce heat & let simmer until liquid thickens, pepper, about 2 mins.
Step #6 Pour potato mixture into prepared dish; shake dish or use fork to distribute potatoes evenly.
Step #7 Gently press down potatoes until submerged in liquid; dot with remaining butter.
Step #8 Bake until top is golden brown (basting once or twice during first 45 mins) about 1 hr 15 mins.