Place cumin, coriander, peppercorns, paprika, cayenne & turmeric into a dry frying pan and toast until just smoking.
Cool slightly before placing into the Thermomix bowl and milling 1 min/speed 10.
Add all remaining ingredients except chicken and blend 10 sec/speed 4. Scrape down and repeat.
Place chicken into large baking dish & slash the skin in large diagonal strips. Rub tandoori mixture into skin & cover chicken for several hours to marinate.
Heat grill to minimum 220°C (or hotter if available). Grill chicken for around 20-30 minutes until well cooked.
With steamed rice, Naan bread or oven fries & a garden salad.