How to Make It
Preheat the oven to 400°. In a small bowl, combine the chopped thyme, chopped rosemary and parsley. Stir in 1 tablespoon of the olive oil and season with salt and pepper.
Using your fingers, gently loosen the skin over the breasts and thighs of the game hens. Stuff 1 heaping tablespoon of the herb mixture under the skin of each bird, pushing the skin around to help distribute the herbs evenly. Season the cavities with salt, then stuff each with 2 thyme sprigs, 1 rosemary sprig half, 1 onion quarter and 2 smashed garlic cloves. Tie the legs of the hens together with kitchen string. Season the outside of the hens with salt and pepper.
In a very large ovenproof skillet, cook the butter over high heat until browned, 2 minutes. Swirl in the remaining 2 tablespoons of olive oil. Add the hens to the skillet, breast down, and cook until golden brown, 5 minutes. Turn the birds and continue to cook until golden brown all over, 15 minutes longer.
Transfer the hens to the oven and roast, breast up, for 1 hour, or until the juices run clear when a thigh is pierced. Remove the strings. Let the hens rest for 5 minutes. Transfer to a platter and serve.