To make the marinade, put the shallots, garlic, coriander roots and ginger in a food processor, whiz to a paste and tip into a bowl.
Dry-fry the coriander seeds, cumin seeds and turmeric until giving off their aroma, then grind to a powder in a spice grinder. Add the ground spices to the garlic paste along with the curry powder, soy sauce, coconut milk, oil, sugar