How to Make It
In a large bowl, combine the pork belly, salt, sage, black pepper and white pepper. Mix well and refrigerate, covered, overnight. Place the meat grinder attachment with the blade, coarse grinding plate and 1-cm stuffing tube in the freezer.
Open one end of the casing and rinse the inside several times with cold water.
Set up the grinder attachment with the coarse plate. Working over a large bowl, gently press the meat through the grinder. Clean the grinder, then set it up again with the stuffing tube attachment (this time, without the blade and coarse grinding plate). Lightly grease the stuffing tube. Slide the casing on the stuffing tube, leaving about 2 inches of overhang. With the mixer on low speed, pass a handful of meat through the machine. Once the sausage begins to collect in the casing, form the sausage with your hands and tie the end of the casing in a knot. Increase the speed and pass the remaining meat through the stuffing tube, holding the sausage loosely in one hand to control how tightly the sausage is packed.
Lay the sausage on a damp surface. Twist the sausage into 4-inch links. Remove any air pockets by piercing the sausages with a needle.
The sausages can be refrigerated for up to 1 week, or frozen for up to 3 months. Serve sausages poached, grilled or pan-fried.