Some sweet facts about sweet potatoes

They're sweet, but with no artificial sugar, packed with vitamin A (one large contains more than 34,000 IU), containing almost as much potassium as bananas (422 mg vs. 542 mg) and a good-for-you dose of dietary fiber (6 g per 6 ounces). Hard to believe this describes a simple sweet potato.

As the season of the sweet potato quickly descends upon us, let's take a moment to consider sweet potatoes.

Some folks use the term yam and sweet potato interchangeably, but they are not the same. The sweet potato (Ipomoea balatas) is the root of a vine in the morning glory family; where a yam (Dioscorea species) is the tuber of a tropical vine.

Yams have more calories than sweet potatoes (116 vs. 90 per 100 grams) and deliver 16 percent more fiber and 7 more grams of carbs. Their fat content is equal and even though some believe yams are sweeter, sweet potatoes yield 13 times more natural sugar than yams (6.48 grams vs. 0.49 grams).

Yams originated in Africa; sweet potatoes in South America. While yams date back to 50,000 B.C., they are mere babies when compared to sweet potatoes that can trace their origins to prehistoric times.

While sweet potatoes overflow supermarket bins, true yams are coy little devils that can be difficult to locate. If you want the real thing, stop in to a Latin American or Caribbean market.

So if sweet potatoes aren't related to yams, they must be related to regular potatoes, right?

Well, no. America's favorite, white-fleshed potatoes fall into an entirely different genus - Solanum tuberosum.

Despite the differences, they're are some similarities, at lease when it comes to uses.

Like making baked potatoes.

Baking intensifies a sweet potato's sweetness, so instead of needing a mountain of sour cream and butter to make it palatable, it simply needs a smear of no trans fat, soft tub margarine and a sprinkle of sea salt and black pepper. Shirley Corriher, food scientist and cookbook author, once told me that she prefers using mashed sweet potatoes in cake batters as a substitute for some of the shortening. It turned out that the high-fiber and low-moisture content of a baked, cooled and mashed sweet potato makes it ideal to replace half to three-quarters of the shortening in some cakes, brownies and many muffins. If you've tried drained applesauce as a shortening substitute, bake an extra sweet potato and give Corriher's theory a trial run.

Since chilling sweet potatoes diminishes the flavor, do your best to purchase sweet potatoes that have not been chilled. Don't store sweet potatoes in your refrigerator, either. A cool, dry, well-ventilated place, out of plastic bags will do just fine.

A few years ago I started making a sweet and white potato casserole that looked wonderful on my Thanksgiving table, tasted great and delivered few fat calories. Over the past year, I've tweaked that recipe (adding fat-free half-and-half for some of the milk, adding bay leaves to the water in which the onions and potatoes cook and kicked-up the seasoning) and made it even better. Give it a try this holiday season; I'm certain you won't be disappointed.

• Don Mauer welcomes questions, shared recipes and makeover requests for your favorite dishes. Address them to Don Mauer, Daily Herald Food section, P.O. Box 280, Arlington Heights, IL 60006 or don@theleanwizard.com.

Sweet and White Potato Casserole

3 cups thinly sliced yellow onions

2 bay leaves

4½ cups thinly sliced, peeled Yukon Gold potatoes

4½ cups thinly sliced, peeled sweet potatoes

2 tablespoons unsalted butter

7 tablespoons all-purpose, unbleached flour

1 teaspoon salt

½ teaspoon ground mustard

½ teaspoon fresh ground black pepper

½ teaspoon sweet paprika, plus more for garnish (or smoked paprika)

1½ low-fat milk

2 cups fat-free half-and-half

4 tablespoons chopped fresh parsley leaves (Italian flat-leaf preferred)

1 teaspoon minced fresh thyme leaves

Place oven rack in the center position and heat oven to 400 degrees. Lightly spray a 13-by-9-inch casserole dish with vegetable oil. Set aside.

Bring a large pot of salted water to the boil. Add bay leaves, onions and potatoes and boil, covered, for 5 minutes. Drain; discard bay leaves.

Meanwhile, place a 2-quart saucepan over low heat and add butter. When it melts, stir in flour, salt, mustard, pepper and paprika. Whisk in milk and half-and-half and cook, whisking constantly, until smooth and thickened (add more milk if too thick). Remove from the heat, whisk in parsley and thyme; set aside.

In the prepared casserole, arrange one-third of the potatoes and onions; pour over one-third of sauce. Repeat with half of remaining potatoes and onions, and half of remaining sauce. Top with remaining potatoes and sauce. Dust generously with paprika (if you use smoked paprika dust with a lighter touch). Bake, uncovered 35 minutes or until tender and the top browns slightly.

Serves 10.

Nutrition values per serving: 202 calories (16.3 percent from fat), 3.7 g fat (1.9 g saturated), 36.8 g carbohydrate, 7.7 g protein, 9.7 mg cholesterol, 291 mg sodium.