Preheat the oven to 375°F.
Fry the chicken in a snug-fitting pot with a little oil, butter, or fat until golden, turning the chicken as best you can to get an even color all over.
Remove from the heat and put the chicken on a plate. You'll be left with fryings at the bottom of the pan which may give you a lovely caramel flavor later on.
Put the milk in the pan and mix with the fryings on the bottom of the pan. Add the cinnamon stick, sage leaves, lemon juice, unpeeled garlic cloves and stir. Put your chicken breast-side down back in the pot.
Cover and cook in the hot oven for 1 hour 30 minutes, or until cooked through. The lemon juice will sort of curdle the milk, making a tasty sauce.
Take the chicken out of the pan and put on a plate. Let it rest.
To thicken the sauce in the pan, put the pan on the stove top and bring the sauce to a boil. Meanwhile, take 1/2 cup water and add 1/4 cup flour. Stir until it is mostly smooth. Once the sauce is (close to) boiling, add the flour and water mixture, stirring all the time. When it thickens, turn off the heat.
Divide the chicken as you normally would. Put it on the plates. Spoon the white gravy over the meat. Serve with rice or potatoes and put the gravy over them as well.