1 Mix the sausage meat, sage, onion and egg together in a large bowl and place in the fridge for at least 1 hour.
2 Place the sugar and butter in a large frying pan and melt very gently, until the sugar is dissolved.
3 Increase the heat, add the apple slices and cook for 5-6 minutes, or until softened and golden.
4 Shape the sausage meat into 5 burgers and place under a hot grill, until cooked and browned.
5 Top with the Cheddar, and grill until slightly melted. Halve the burger buns and spread with mayonnaise.
6 Fill the buns with the sausage burgers and top with apple, watercress and bun lids.