Preheat your oven to 350°F. Lightly coat a 9x11 baking dish with non-stick spray.
Clean the Cornish hens by removing any giblets. Using kitchen shears, cut down each side of the backbone, starting at the neck and cutting down to the tail. Remove the backbone and flatten the hens.
Season the front and back of each hen with seasoning salt, black pepper, garlic powder, and onion powder.
In a small bowl, combine the butter, fresh thyme, rosemary, and ground sage.
Loosen the skin of the hens and spread the herb butter evenly under the skin, reserving 2 tablespoons for basting.
Add the chicken stock to the baking dish. Place the hens in the oven and bake for about 1 hour, basting with the pan juices after 30 minutes.
While the Cornish hens roast, you can prepare the savory bacon gravy to serve alongside. (The link to my detailed recipe is in the notes section below.)
The hens are ready when they turn golden brown, and the wings or legs feel tender when gently pulled.