1) Heat the oil in a heavy pan and fry the onions, garlic
and ginger for 5 mins. Add the chillis and cook for 2
mins more.
2) Add the remaining spices then stir for 30 secs. Stir in
the tomatoes, stock, lemon juice and rind. Bring to the
boil then simmer uncovered for 30 mins.
3) Discard the lemon rind. The sauce is now ready to use or
may be kept in a fridge for several days.