3 tablespoons butter
2 medium-sized onions, thinly sliced
3 cloves garlic, minced
2 bay leaves
1/4 teaspoon freshly-grated nutmeg
1 1/4 tablespoons salt, divided
1 teaspoon freshly-ground pepper, divided
1 1/4 cups heavy cream
1/2 cup milk
1 cup (about 3 ounces) freshly-grated Asiago or Parmesan Cheese
1 cup plain dry bread crumbs
2 tablespoons extra-virgin olive oil
2 1/2 tablespoons finely-shredded fresh sage leaves, divided
2 1/2 pounds medium-size Russet potatoes, peeled and sliced 1/8-inch thick*
* Russet baking potatoes are the preferred. Avoid using "new potatoes", redskins, or any other high moisture potato. Russet potatoes have a high starch content and bake well. They also make top-quality mashed potatoes. Russet potatoes are often called Idaho potatoes after the state that leas in their production. Choose potatoes that feel firm and not spongy. Avoid those with eyes or dark spots, which are a sign of age.
Preheat oven to 400 degrees F. Adjust oven rack to middle of the oven.
Peel potatoes and slice into approximately 1/8-inch thick slices. If you have an mandoline slicer, this is the perfect time to use it - otherwise use a sharp knife. You want your potato slices to be as even as possible.
In a large heavy saucepan over medium heat, melt butter. Add sliced onions and cook, stirring, until golden or approximately 8 minutes. Add garlic, bay leaves, nutmeg, 1 tablespoon salt, and 3/4 teaspoon pepper; cook for 30 seconds. Add cream and milk; bring just to a boil. Remove from heat, cover, and let stand for 5 minutes. After 5 minutes, remove the bay leaves from the onion mixture and stir in 2 tablespoons sage; set aside.
In a bowl, toss the Asiago or Parmesan cheese with the bread crumbs, olive oil, 1/2 tablespoon remaining shredded sage, 1/4 teaspoon salt, and 1/4 teaspoon pepper. Set aside.
In a large bowl, place the sliced potatoes; add prepared onion mixture and toss gently.
Spread 1/2 of the potato-onion mixture in a 2-quart baking dish; sprinkle 2/3 cup of the cheese/bread crumb mixture over the top. Cover with the remaining potatoes and press firmly to pack them down. Spoon the remaining liquid over the potatoes and cover with remaining cheese/bread crumbs.
Bake approximately 1 hour or until the potatoes are tender and the top is golden (scalloped potatoes are done when potatoes are tender but hold their shape when portioned). If the potatoes brown too quickly, loosely cover the dish with aluminum foil.
Make Ahead Tips: The dish can be assembled up to 4 hours ahead, covered with a tight lid or aluminum foil, and refrigerated. Let sit at room temperature, covered, while the oven heats. NOTE: If potatoes are not covered completely, they are going to make contact with air and, while cooling, they will slowly begin to get a dark color.
Once cooked, you can keep the cooked scalloped potatoes, covered, in a warm oven for up to 1 hour before serving. Re-warm in the oven before serving, if necessary.
Makes 8 to 10 servings.