Coat the chicken with a drop of olive oil and season with salt. Place the chicken in a large casserole dish and roast it in the oven at 200°c for 45 minutes.
Wash the potatoes and cut big ones in half. Clean the green pepper and cut it into chunks. Remove the skin of the chorizo and slice it into slices.
After 45 minutes take the chicken out of the oven and remove all excess fat. Add the butter and potatoes and put back in the oven for 30 minutes. Add the green pepper, chorizo, and rosemary and roast for another 15 minutes.