First make the brat seasoning by combining equal parts of the sea salt, white pepper, celery seed, mace and 1 tablespoon of the sage. Set aside.
Using a meat grinder or food mixer with a sausage grinding attachment, grind the pork butt and jowl fat twice until combined and a smooth consistency.
Add 2 ounces of the prepared brat seasoning to the ice water and mix until it forms an emulsion then add to the pork mix.
Knot one end of the casing and attach the casing to the mixer sausage making attachment, fill the casings until approximately 3 inches in length, twist and repeat to the desired sausage amount and then tie a knot to secure the last sausage.
Poach the sausages in 75-77°C water until the internal temperature reaches 65°C (roughly 5 minutes). Put sausages on a grill/under a broiler to finish.