Cornish hens resemble miniature chickens and are a very flavorful cross breed between a Plymouth Rock hen and a Cornish game cock. They weigh between 1 and 2 pounds and can be successfully grilled in a shorter amount of time than it takes to cook a whole chicken. The trick, according to Andrew Schloss, David Joachim and Alison Miksch, authors of "Mastering the Grill: The Owner's Manual for Outdoor Cooking," is to marinate the Cornish hen, butterfly it and grill it over direct heat.
Rinse your Cornish hens with cool water and dry them with a paper towel.
Butterfly each Cornish hen. Lay the hens on a cutting board with their back sides up. Use poultry shears to cut along one side of a hen's backbone. Cut along the other side of the backbone and discard the bones. Turn the hen over and press on the breastbone to flatten the bird.
Whisk olive oil, white wine, garlic and rosemary together in a marinating dish.
Add the butterflied Cornish hens and spoon the mixture over them to coat. Marinate the birds for four to eight hours, turning and basting them occasionally. Use a turkey baster as necessary.
Preheat your outdoor grill to medium heat.
Use a pair of tongs to place each Cornish hen on the grill, breast side up. Brush the meat with the leftover marinade and discard the rest.
Flip the Cornish hens over after 15 minutes.
Cook the hens for an additional 15 minutes, or until an instant-read meat thermometer registers 180 degrees Fahrenheit.
Remove the hens to a serving platter and let them rest for five minutes before serving.