For the demi-glace
Rinse bones and wings with plenty of cold water and remove any remaining offal. Place in a saucepan, preferably tall and narrow, with the water and bring to the boil, removing any foam as it forms. Lower the temperature so that the stock bubbles very slowly and “lazily”. From reaching boiling point, the total cooking time is 3 hours. During the first half hour, you will have to skim constantly and later carefully remove any fat which gathers on the surface. After two hours of boiling, add the onion, carrot, garlic, bay leaf and tomato paste. At 2 and ¾ hours, add the parsley and thyme. After 3 hours of simmering, remove from the heat and strain using a fine sieve. Place in a pot and simmer until the stock reduces to 1/3 of its initial volume. Strain again through a fine sieve, cool rapidly and store in the fridge. As soon as the stock has solidified, remove the fat that has gathered on the surface.