Question--plain cast iron or enameled cast iron? Plain cast iron could be a problem here, especially if you want to make a sauce.
My best recipe won't do you if you want to cook today. You really need a meat thermometer ot get it right.
I brine the chicken (soak at least 4 hours in salt water). Drain & rinse. Pat dry.
Preheat oven to 375F/190C. Put pan in oven heat while you do the prep.
Then I mix soft butter with whatever herbs I have or want. Thyme, rosemary, sage are good. Or pureed garlic. Slip my fingers under the skin to loosen it, then put the butter under the skin. Massage it around. Rub the chicken with my greasy hands. I might or might not put garlic or a cut lemon half in the cavity.
Fold wings under the back, tie legs together. Cover the breast of the chicken tightly with aluminum foil. This is going to keep the breast from overcooking.
Take out pan & put a rack in the pan (if you don't have a decent rack, make a snake out of aluminum foil & coil it up. Put chicken on rack & put in oven. After 15 minutes, remove foil & pour about a half cut of water in the bottom.
Now, do nothing. No basting or fussing.
Check with a thermometer after about 45 minutes. A 2-kilo bird will take about an hour to cook. It is ready when the breast temperature is about 160F/70C. Remove chicken, put on platter, tent with foil & let it rest for 20 minutes before serving.
Deglaze pan to make sauce or gravy.
