Swedish Christmas Sausage

• 6 yards hog casings
• 3 onions (finely chopped)
• 1,400 gr beef (lean)
• 600 ml scalded milk
• 325 gr beef
• 300 gr mashed potatoes
• 120 ml water
• 26 gr salt
• 8 gr pepper (ground)
• 4 gr allspice (ground)