Not sure what creme fraiche is or why you should care?

Consider it a relative of sour cream. Except that while both are white, thick and creamy, creme fraiche is the richer, sexier and more talented relative.

Here's the deal. Like yogurt, sour cream and creme fraiche are dairy products produced thanks to the miracle of friendly bacteria. But while yogurt is made by adding those bacteria to milk, sour cream and creme fraiche are made by adding them to cream.

So what's the difference? Sour cream is made from cream that is 20 percent fat; creme fraiche sports an even more succulent 30 percent.

That may not sound like a big difference, but it matters in both taste and versatility. That extra fat turns creme fraiche into a kitchen workhorse.

But first, taste. While sour cream tastes, well... sour, creme fraiche is rich and tart. And as a byproduct of the bacteria added to produce it, creme fraiche tends to make other foods taste buttery.

But unlike yogurt, creme fraiche isn't particularly acidic (so it's not great for marinades).

The trouble with sour cream is that you have to be very careful when cooking with it. Heat it too much and it curdles. Ditto for yogurt. But the higher fat content of creme fraiche means you can boil with abandon and it won't separate. This makes it ideal for soups, sauces and simmered dishes.

It will, however, liquefy. That means that if you add it to the top of something, then toss it under the broiler (as in the recipe for croque monsieur below), or even just dollop it onto something hot, it will melt.

In France, where it originates, creme fraiche often is used in sauces for vegetables, particularly green beans and cauliflower, as well as in salad dressings, soups and pastries, and to top fresh fruit. It's sometimes used to make caramels and even is added to coffee and cocktails.

It's easy to make your own, but let's be honest, most of us won't. Add a tablespoon of cultured buttermilk to 1 cup of cream and let it sit in a cool room for up to 24 hours, or until very thick. Refrigerate for several weeks. Creme fraiche is widely available at most grocers in the U.S. It usually is found alongside the better cheeses, though it sometimes will be near the sour cream. It keeps, refrigerated, for about a month.

For more ideas for using creme fraiche, check out the Off the Beaten Aisle column over on Food Network: http://bit.ly/QyDefT

Croque monsieur

Adding cornstarch to the creme fraiche allows you to broil it without it liquefying. It's an easy and delicious substitute for the traditional roux-based sauce used in croque monsieur.

Start to finish: 15 minutes

Servings: 2

1/2 cup creme fraiche

1/2 cup grated Parmesan cheese, divided

1/4 cup grated cheddar

1 tablespoon cornstarch

1/2 teaspoon garlic powder

1/2 teaspoon hot sauce

1/2 teaspoon ground black pepper

1/4 teaspoon salt

Pinch nutmeg

2 tablespoons Dijon mustard

4 slices sandwich bread

4 slices gruyere cheese

8 slices smoked deli ham

1 tablespoon butter, softened

Heat the oven to 350 degrees.

In a small bowl, mix together the creme fraiche, 1/4 cup of the Parmesan, the cheddar, cornstarch, garlic powder, hot sauce, pepper, salt and nutmeg. Set aside.

Spread a quarter of the mustard evenly over one side of each slice of bread. Top each with 1 slice of cheese and 2 slices of ham. Overturn 2 of the stacks onto the others to make 2 sandwiches. Spread the butter over one side of each sandwich.

Arrange the sandwiches on a baking sheet, buttered side up, and bake for 5 minutes. Remove the baking sheet from the oven. Set the oven to broil.

Flip the sandwiches and spoon half of the creme fraiche mixture over the top of each sandwich. Top with the remaining Parmesan.

Broil for 1 to 2 minutes, or until the cheese is melted and just starts to brown.

Nutrition information per serving (values are rounded to the nearest whole number): 820 calories; 410 calories from fat (0 percent of total calories); 46 g fat (25 g saturated; 0 g trans fats); 160 mg cholesterol; 43 g carbohydrate; 61 g protein; 4 g fiber; 2,620 mg sodium.

J.M. Hirsch is the national food editor for The Associated Press.