heat the oil in a saucepan and add the diced onion. Stir around to coat the onion in the oil, put a lid on the pan, turn the heat down low and leave to cook for 15 minutes.
take the lid off the pan and continue to cook, stirring regularly, until the onions start to turn deep brown.
Add the chopped garlic and ginger and cook for 40 seconds.
Add the diced carrot and pepper, turn up the heat slightly and continue to cook for 5 minutes, stirring and scraping the bottom of the pan to remove all the caramelised juices.
Add the hotel gravy masala or spice mix and cook for around 40 seconds.
Add the tomato puree, stir into the mixture and cook for 30 seconds or so.
Add the tinned tomatoes, optional coriander and water, bring to a simmer, and cook gently for around 15 - 20 minutes or until the carrot is soft enough to blend.
Let the gravy cool a little before blitzing with a hand blender until really smooth.
To use the gravy, add to fried garlic, ginger, (and in some recipes, onion) and spices, bring to a simmer before adding your main ingredient. This gravy can be used in many recipes that require a hotel gravy or base sauce, it doesn't need thinning out though and can be used to cook more than just a single or double portion as no rapid reduction is needed.