Preheat the oven to 400 degrees F.

In a small bowl, combine the butter, lemon juice, rosemary, parsley, garlic, and parmesan. Reserve about 2 tablespoons of the mixture for later.

Pat the hens dry with paper towels and generously brush the Cornish hens with the lemon garlic butter mixture, inside and out. Season with salt/pepper.

Place the hens in a roasting pan and arrange the lemon slices and rosemary sprigs around the hens. Bake for about 50 to 60 minutes or until golden brown and completely cooked through.

Remove the hens from the oven and brush with the remaining marinade. Let them rest for 20 minutes before serving and enjoy.