In a small bowl, combine all of the dry ingredients and set aside.
Prep the Cornish hens: pat dry with kitchen towels, then stuff each Cornish hen cavity with a piece of onion, garlic, lemon, and a sprig of rosemary. Truss the legs with butcher twine and tuck the wings behind the bird.
Drizzle with half of the olive oil, then season thoroughly with the dry rub.
In a 9x13-inch roasting dish, add the onion, garlic cloves, lemon, and rosemary sprigs. Place the Cornish hens on top of the aromatics, and drizzle with the rest of the olive oil.
Add ⅓ a cup of water or chicken stock to the pan.
Roast uncovered in the oven for 1 hour or until the internal temperature reaches 180°F/83°C.
Remove the Cornish Hens to a plate, and tent with foil to rest. Pour the juices into a small saucepan, and reduce for 5 minutes to create a sauce.
Cut each Cornish hen in half and serve with mashed potatoes, rice, or roasted/steamed vegetables. Drizzle some sauce, and enjoy!
Trussing the legs is optional, but I find it holds the aromatics better and makes a nicer presentation.
Change things up, and add potatoes and carrots with the aromatics to roast and serve with the hens.
Take it to the next level by adding softened butter with minced garlic under the breast skin.
If your Cornish hens are larger, you might need to cook them for a bit longer. Always check the internal temperature (must reach at least 165°F) to make sure the Cornish hens are cooked and safe to eat.
If the sauce does not thicken easily, thicken with corn starch slurry in a saucepan over medium heat (1 teaspoon of corn starch mixed with 1 teaspoon of liquid, add that to the sauce and whisk to thicken).