Heat olive oil in a non stick pan and cook the chopped onion and garlic in it till the onion is soft and translucent.
Stir in the cumin, turmeric, cinnamon, coriander, cayenne and paprika.
Continue stirring over medium heat for 2-3 minutes, then add vegetable broth, tomato puree and currants.
Simmer the sauce for 10 minutes.
Remove the sauce from heat and stir in fresh lemon (or lime) juice to your taste.
If not using immediately and planning to reheat before serving, wait to add citrus juice at the last minute.
To cook the couscous, heat the broth, water, butter and salt together in a medium skillet till the liquid boils.
Reduce to a simmer, add the couscous, cover the skillet tightly and leave on the lowest heat for 5 minutes.
Remove the pan from the heat an leave it covered for another couple of minutes before fluffing with a fork.
(If using instant couscous, check package directions - you may not need to keep it on heat after boiling, but just cover and wait till liquid is absorbed - just see if liquid amounts match what is mentioned on the package).