In a medium bowl, mix together the cubed pork shoulder, garlic, salt and pepper. Place on a clean smooth surface and knead for at least 10 or 15 minutes. This is worthwhile as the longer you can knead the mixture - the more tender your sausage will be.
Soak the sausage casings in water for 1 or 2 minutes. Rinse the casings by sliding over the tap. Slide the casing all the way up onto the spout of a sausage stuffing funnel. Press meat through the funnel into the casing carefully so that no air bubbles get inside. Sausages should be plump. Twist periodically to form links.
Place sausages in a large pot with enough water to cover them. Bring to the boil, then reduce heat to low, cover the pot, and simmer for 1 hour and 15 minutes. They can be frozen after cooling. Use as you would shop bought sausage.