Frank Costanza was right after all. “Seinfeld” fans will recall the 1996 episode when the crusty Costanza, played by Jerry Stiller, pointed to the bird on his plate and asked, “What is this thing anyway?” Told it’s a “Cornish game hen” by his son’s snooty prospective in-laws, he replied, “What is that? Like a little chicken?”

“It’s not a little chicken. Little chicken. Ha. Ha. It’s a game bird, Dad,” interjected his clearly mortified son, George, portrayed by Jason Alexander. As you might guess, the sitcom dinner went rapidly downhill from there.

But a Cornish hen is a little chicken. The U.S. Department of Agriculture currently defines it as “a young immature chicken (usually 5 to 6 weeks of age), weighing not more than 2 pounds ready-to-cook weight, which was prepared from a Cornish chicken or the progeny of a Cornish chicken crossed with another breed of chicken.” Though called a hen, the bird can be male or female.

In 2011, the USDA’s Food Safety and Inspection Service lowered the age definition for a Cornish hen from 5 to 6 weeks to less than 5 weeks. This final rule takes effect in 2014, said Cathy Cochran, a USDA spokeswoman in Washington.

Alphonsine “Therese” Makowsky is credited with originally breeding the Cornish hen at a farm in Pomfret, Conn., that she owned with her husband, the artist Jacques Makowsky.

Her 2005 obituary in the San Francisco Chronicle — she was living in Danville, Calif., at the time of her death at age 92 — noted the couple had been raising and selling African guinea hens until a 1949 fire destroyed their stock. In response, the obit reported, she came up with the idea of “cross-breeding the Cornish game cocks with various chicken and game birds, including a White Plymouth Rock hen,” to create the Cornish hen. It quickly supplanted the couple’s African guinea hens in popularity, the Chronicle noted.

Cornish hens proved so chic that Victor Borge, the musical comedian, began breeding them at his home in Southbury, Conn., according to a 1958 story in The Hartford Courant. The writer of a 1960 New York Times article, “Food: Yankee hen is a hit abroad; Even a Frenchman finds Connecticut bird a treat,” marveled at how far the little birds had flown in just 11 years, from a Connecticut farm to being “served in elegant establishments around the world.” In the mid 1960s, Tyson Foods began selling Cornish hens.

The Springdale, Ark.-based poultry giant is the leading producer today, marketing an estimated two-thirds of Cornish hens produced in the United States, according to Brady Tackett, a company spokesman.

Cornish hens deliciously prove the adage: Good things do come in small packages. Savvy hosts can capitalize on that to easily create a special Christmas or New Year’s Eve dinner.

One, the diminutive hen is so distinctive in size that many people might mistake them for game birds instead of ordinary chickens. Two, they look so darn posh preening on the plate, guests will feel rather spoiled when you serve them.

“They’re an impressive kind of entertaining dish,” said Nathalie Dupree, the Charleston, S.C.-based cookbook author and television cooking show host. “They look a little uptown even though they are just chicken.”

Dupree is a big fan of the birds, also known as Rock Cornish game hens, Cornish chicken or Cornish game hens. They remind her of what chickens used to look like during her childhood before the age of supersized everything.

“I’d rather cook two Cornish hens than one humongous chicken,” she said.

Size matters also to Robb Walsh, author of “Texas Eats: The New Lone Star Heritage Cookbook.” The Houston writer developed a recipe using Cornish hens in place of German spring chickens because he misses having the variety of size options with poultry that French and German consumers enjoy.

“Cornish hens are a reminder of when we had a choice,” he said.

Being so small, the birds cook fast. Dupree says she throws a bird in the oven and gives it a quick glaze of marmalade or pepper jelly right before the finish. She doesn’t stuff the cavity, but she does like to put some seasoned ricotta cheese under the skin, a trick inspired by the late Richard Olney, a food writer, cook and editor.

A whole hen is too much of a serving for Dupree, but she doesn’t want to risk the embarrassment of skimpy portions for guests. Her solution?

“I roast an extra hen for every few people,” she writes in her latest book, “Mastering the Art of Southern Cooking” (Gibbs Smith, $45), co-authored with Cynthia Graubart, “and then cut the extras in quarters, available for second (or third!) helpings.”