Nutritional yeast is an ingredient used in many vegetarian recipes because it's a source of protein and B vitamins. It adds a nutty, cheesy flavor to many dishes such as casseroles and gratins. Another common use is to sprinkle the yeast on popcorn and cooked vegetables.

It's yellowish in color and sold in flake or powder forms.

Nutritional yeast is similar to brewer's yeast: Both come from the same strain of yeast and are used as nutritional supplements. But brewer's yeast is a byproduct of beer-making, according to the Cook's Thesaurus, and that's what makes it bitter. So don't substitute one for the other.

And don't confuse nutritional yeast with yeast used in baking. Nutritional yeast is not active, so it is nonleavening. It's pasteurized, which deactivates it.

Once nutritional yeast is deactivated, it becomes a good source of nutrients, the thesaurus says.

Most health-food stores carry nutritional yeast. There are several brands and container sizes of nutritional yeast. Prices range from $6.50 for a 4 1/2-ounce container to $18 for 16 ounces.

If you're new to nutritional yeast, try using it in this Mac and Cheese-Style Cauliflower recipe adapted from Vegetarian Times magazine's January/February 2012 issue.

Mac and Cheese-Style Cauliflower

Makes 8 1-cup servings. Prep time: 15 minutes. Total time: 1 hour.

     8     heaping cups cauliflower florets

     2     tablespoons butter or margarine

     1     shallot, peeled, minced

     2     cloves garlic, peeled, minced

     3     tablespoons all-purpose flour

     2    cups 1 percent low-fat milk

     2    cups grated extra-sharp cheddar cheese

     1/2  cup nutritional yeast (optional)

     1     pinch cayenne pepper

     2    egg yolks

     1 1/2     cups fresh bread crumbs or panko bread crumbs

     Fresh chopped parsley or snipped chives for garnish (optional)

HEAT oven to 350°. Coat the bottom of a 13- by 9-inch baking dish with cooking spray and set aside.

BRING a large pot of salted water to a boil. Add cauliflower florets and boil until just tender. Drain and reserve 1 cup cooking liquid; set aside. In the same pot, melt the butter over medium heat.

ADD shallot and garlic and sauté about 2 minutes. Whisk in flour and cook 1 minute, stirring constantly. Whisk in milk and 1/2 cup of the reserved cooking liquid; cook 7 to 10 minutes or until sauce is thickened, whisking constantly. If the sauce is too thick at this point, add more of the reserved cooking liquid.

REMOVE from heat and stir in cheese, nutritional yeast, cayenne pepper and egg yolks until cheese is melted. Fold in cauliflower.

SPREAD cauliflower mixture in the baking dish. Sprinkle with bread crumbs. Spray bread crumbs with cooking spray. Bake 30 minutes or until casserole is hot and bubbly and bread crumbs are crisp and brown. Garnish with fresh chopped parsley or chives, if desired.

Nutritional information: Per serving: 273 calories (53 percent from fat), 16 grams fat (9 grams saturated fat), 18 grams carbohydrates, 16 grams protein, 314 milligrams sodium, 94 milligrams cholesterol, 4 grams fiber.