Preheat the oven to 375°, and find a snug-fitting pot for the chicken. Season it generously all over, and fry it in the butter and a little olive oil, turning the chicken to get an even color all over, until golden.
Remove from the heat, put the chicken on a plate, and throw away the oil and butter left in the pot. This will leave you with tasty sticky goodness at the bottom of the pan, which will give you a lovely caramel flavor later on.
Put your chicken back in the pot with the rest of the ingredients, and cook in the preheated oven for 1½ hours. Baste with the cooking juice when you remember. The lemon zest will sort of split the milk, making a sauce that is absolutely fantastic.
To serve, pull the meat off the bones and divide it onto your plates. Spoon over plenty of juice and the little curds.