Marinating Cornish hens before cooking them improves their flavor and tenderizes the meat. You can mix a simple batch of marinade with ingredients you probably have on hand or make a bigger batch and use the extra for basting or for seasoning potatoes or vegetables. Any herb, spice or marinade appropriate for chicken also will work well with Cornish hens. Cut the birds in half to shorten the time needed for marinating and cooking.
Remove the package of giblets from the cavity of the Cornish hens, if necessary.
Rinse the Cornish hens in cool running water. Pat the birds dry with paper towels.
Mix the garlic, rosemary, kosher salt, black pepper, lemon juice and olive oil in a glass dish. Make extra and set aside in a separate container if you wish to use these same seasonings to baste the hens during cooking.
Place the hens in the glass dish and spoon some of the marinade over the tops of the hens. Make certain the marinade penetrates the cavity of each bird. Cover.
Refrigerate the marinating hens for at least one hour and up to 24 hours. Do not marinate at room temperature.
Remove the hens from the marinade before cooking and then discard the marinade. Use only fresh marinade to baste the hens.