1. In a mixing bowl, add all ingredients under marinade in a mixing bowl and mix evenly.
2. Coat lamb shoulder with marinade and refrigerate overnight, flipping over halfway through, 24 hours would be best.
3. Remove lamb 2 hours before cooking to let it set to room temperature.
4. Roast in a 220°C oven for 15 minutes.
5. Remove from the oven and turn the heat down to 175°C. Brush lamb with remaining marinade.
6. Roast lamb for another 25 - 30 minutes measuring internal temperature of 60°C.
7. Leave meat to rest for 15 minutes.
8. Add marinade into a saucepan and reduce until thick for about 5 minutes.
9. Serve lamb with creamy mashed potatoes and carve.
10. Garnish with coriander
