Over a high heat, reduce the tea to approx. 200 ml along with all the other ingredients up to and including the sugar. Strain the liquid, return to the pan and bring to the boil. Stir the cornflour into the hot liquid, cook for approx. 2 mins.
Remove the pan from the heat. Gradually add the butter while stirring. Return the pan to the hob a few times to barely warm the sauce; it must not boil. Stir until the sauce is creamy, season.
Cut a cross into the fatty layer of the duck breasts and season the meat. Place the duck breasts in a cold frying pan, with the fatty layer facing down. Heat the pan and fry the duck breasts for approx. 7 mins. over a medium heat until the fat turns crispy. Turn the duck breasts and fry for approx. 7 mins.