Preheat oven to 400°. (It is imperative that oven is fully preheated prior to cooking hens.)
In a large bowl, combine olive oil, salt, pepper, rosemary, and garlic. Place hens in bowl, and coat thoroughly with olive oil mixture.
Transfer hens and olive oil mixture to a large roasting pan.
Bake for 30 minutes. Reduce oven temperature to 375°, and baste hens with olive oil mixture. Bake for 25 minutes. Using tongs, carefully turn hens over; bake for 15 minutes. Baste in olive oil mixture. Increase temperature to broil; broil 5 to 6 inches from heat for 5 minutes. Turn hens, and broil 5 minutes more. Cook until a meat thermometer inserted in thickest portion registers 180°. Remove from oven, and let cool slightly. Serve with Roasted Fingerling Potatoes and Sautéed Mushrooms. Garnish with rosemary, if desired.
Recipe by Victoria at https://victoriamag.com/roasted-cornish-hens-recipe/