An old-fashioned, peasant image, and long cooking times, may have shadowed these dark leafy greens in the past, but they are now gracing menus at upscale restaurants all over town.

And with good reason - they are among the most nutritious and popular vegetables worldwide.

"Greens are not considered an elegant, rich food," said Althea Zanecosky, registered dietitian and regional spokeswoman for the American Dietetic Association. "But they are making a comeback with the trend toward more traditional foods."

At this time of year, kale, chard and other greens are at their tastiest because cold weather and exposure to frost softens their usual bitter bite and makes them more tender.

They also are an ideal complement and contrast, in flavor and color, for the seasonal squash and sweet potatoes that fill neighboring produce bins through the winter.

And there's a bonus: Winter greens are pretty enough to show off as a centerpiece on the table as well as serve as key ingredients on the menu.

So what if it takes a few minutes more to cook mature winter greens to tenderness compared to milder, more popular spinach? That's no reason to pass up so significant and tasty a food.

There are ways around the slightly bitter taste that deters some diners. Clever cooking techniques and seasoning can soften, even mute, the strong flavors.

Mixing greens to balance those flavors is another way, says Deborah Madison, who has been lauded for her vegetable and vegetarian cooking skills for more than 30 years.

"Kale is robust, chard is a little sweeter, and mustard greens have a tang. Together they make a good combination," said Madison, whose multi-award-winning Vegetarian Cooking for Everyone (Broadway, 1997) was reprised in a 10th-anniversary edition last year.

Seasoning with vinegar, lemon or other citrus also cuts bitter tastes and pungent aromas in these cabbage kin.

"We tend not to cook greens long enough," Madison said during an interview last week. "They look so beautiful, fluffy, green and bright.

"In the spring or summer, you can get younger greens at farmers' markets or pick them fresh from your garden, but in winter, commercially grown greens are more mature with larger, thicker leaves that need to be cooked.

"I'm not a raw-foodist. Tiny first sprouts of kale or beet greens are fine, but in general, winter greens are tough," Madison said (although exposure to cold and frost makes them a bit more tender). "Some people say everything is better raw, but we're not cows. If you enjoy chewing for a long time, go for it. But I believe greens are better cooked. And you can do a lot more with them."

Cooking also makes it easier for our bodies to absorb some good nutrients and antioxidants - the darling carotenoids - in darker greens.

As good as spinach is for us, kale, collards, chard and mustard greens are better.

Those are the most nutrient-rich greens, Zanecosky says.

"They are higher in calcium and are recommended for people who limit their intake of dairy foods. They also are good sources of iron and B vitamins, especially for people who are cutting back on meat in their diet," said Zanecosky, who added:

"As long as they aren't cooked the traditional [Southern] way with a lot of fat, they are very good for you."