1. Preheat oven to 180C. Mix golden syrup, balsamic, mustard and tomato purée to make the toffee glaze. Brush over the sausages and cook in oven for 20 minutes, or until done. You can continue to baste the sausages every 5 minutes for a thicker glaze.
2. Slice the onions thin. Cook in oil on medium to low heat for 20 minutes or until sticky and caramelised. Remove half the onions and set aside for garnish. Add canned tomatoes and salt to the onions, bring to boil, then simmer 5 minutes.
3. Grate the apple and add to the sauce. Simmer a further 15 minutes covered, checking to add a little water if it becomes too dry. When ready blend sauce until smooth.
4. Cut crust off each piece bread. Place in oven at 150C for 1-2 minutes so its firmer and slightly toasted.
5. To serve: Place a sausage on bread slice diagonally, top with tomato sauce and caramelised onion, fold edges together and eat!