1. Put all the ingredients except the water and food colouring into a bowl and beat with a whisk. 2. Add a little water, whisk and repeat the process until you get the desired consistency. I prefer mine a bit thicker than the restaurant version (so it clings to the poppadom a bit more) but still runny enough to pour off a spoon. 3. Carefully add the yellow food colouring powder to the yoghurt mixture. Literally add just the very tip of a spoon at a time. Mix each tiny amount of colouring thoroughly into the yoghurt before you add any more. What’s the right colour? Well, it’s up to you but I like the sauce to look like pale egg yolk. 4. Let the sauce mature for at least 30 minutes before using. 5. Refrigerate until needed.