To make the batter, sift the flour into a large bowl. Add the salt and pepper.
Make a well in the center of the flour and crack in the eggs. Using a wooden spoon, gradually beat the eggs into the flour then slowly beat in the milk until the batter is the consistency of a loose pudding
Strain and push any remaining lumps through a sieve. Cover and leave to stand for 30 minutes, or ideally 3-4 hours.
Preheat the oven to 400F
Place a pot of seasoned water onto the cooktop and bring to a slow bowl.
Wash and slice leeks into coins until you reach the green of the leaf then place coins into your boiling water to blanch for 4 minutes. Then remove and place leeks onto a towel to drain of any access water.
Heat a large non-stick pan and sear the now blanched leeks until perfectly golden brown on one side then set aside, cook the sausages over medium heat until golden-brown all over. Turn off the heat and brush the sausages with the mustard. Set aside.
Place the duck fat into an ovenproof dish and heat in the oven for five minutes or until the dripping is hot and just beginning to smoke.
Add the sausages and seared leeks to the hot dish and pour in the batter. Sprinkle with picked savory then Immediately return the dish to the oven and cook for 35-40 minutes until well-risen and golden-brown.
Serve seasoned with black pepper and a large knob of butter.
