Rusk for Sausage
Most British sausage contains some form of binder. Prior to WWII this was usually in the form of breadcrumbs but, following the introduction of modern bread baking methods, most producers changed to using rusk. Good breadcrumbs from properly cooked home-made bread can still, of course, be used, or rusk can be bought online from suppliers such as Sausagemaking.org, Scobies or Weschenfelder.
Alternatively you can make your own using this recipe which was posted on the Sausagemaking.org Forum:
Rusk
1 lb (450 g) plain/all purpose flour or bread/strong flour
pinch of salt
5 tspns (25 ml) baking powder
6½ - 8¾ fl oz (185 - 250 ml) water
Note: 1 tspn (5 ml) baking soda (sodium bicarbonate) and 2¼ tspns (11¼ ml) cream of tartar may be substituted for the baking powder.
Method
Preheat oven to 450°F (230°C)
Sieve the flour, salt and baking powder together.
Mix it to a smooth, pliable dough using only enouigh of the water to do so.
Roll out lightly to approximately ½" (12 mm) thick then place on a lightly greased tray.
Place in oven on the middle shelf and bake for 10 minutes at 450°F (230°C).
Remove from the oven and using the tines of a fork/or a large knife, split in half along its thickness.
Place back on tray with the opened faces upwards.
Return to oven.
Reduce the heat to 375°F (190°C) and bake for a further 10 minutes, or more until it seems dry.
Remove from oven and allow to cool a little on a wire rack.
Whilst still warm, grind it in a food processor and then dry it further on trays until really dry.
Store in airtight container and use as required.
To save time and effort try using Jewish matzo crackers with equal amounts of ice cold water.