Make the Yorkshire pudding batter by combing the flour, eggs and a splash of milk whisk until smooth then beat in the remaining milk. Pass through a sieve and rest in a fridge until ready to use
Fry thinly sliced onion in beef fat until golden and crispy, medium low heat for 12-15 mins should do it. Drain them off but keep the beef fat
To make the gravy soften the shallot, celery and carrots in a pan with a pinch of salt. Add the bay, thyme and rosemary then add the wine and reduce by ⅔ then add the stocks and simmer/reduce a low/medium heat for 1 hour. Strain this through a sieve pressing all the flavour out then reduce again until happy. Finish the gravy with Worcestershire sauce, butter and a little sherry vinegar
Use the infused beef fat from earlier to brown the sausages then remove and heat the pan/tray in an oven at 200c for 10 mins before pouring in the batter adding the sausages and baking for 35-40 mins. Don't open the oven door.
Serve with gravy, beef fat onions and chopped chives
