Curry in a hurry - tamato base for Indian curries

I like to prepare this curry base and freeze it in portions, making it very easy to put together an Indian lentil/bean curry in a hurry! I usually make double or more of this recipe.

Heat a heavy-based saucepan, add 2 tablespoons of oil.
Fry ½ teaspoon of mustard seeds, as soon as they start popping, add sliced onion (½ medium sized)
When the onion is translucent/clear add your spices:
½ teaspoon red chilli powder
¼ teaspoon turmeric powder
½ teaspoon cumin powder
¼ teaspoon coriander powder
and a pinch of cinnamon
Allow the spices to fry in the oil for a minute.
Then add your tomatoes. These can be chopped fresh (3 large) or canned* (1-2 cans of whole/diced) which when cooked you can blend with a stick blender to puree.
I also add ½ teaspoon of ginger paste and the same of garlic paste (ground fresh is best tho!)
I allow the tomatoes to cook for 10-15minutes and then blend them into a sauce which I simmer for another 5-10minutes.

At the start of the recipe before you add the onion; you have the option of adding fresh curry leaves (available from Indian stores or good grocers) for a more authentic flavour and dry red whole chillies if you like spicy food.

Once cooled, I freeze this base in portions (½ can of tomato per portion). When in a super hurry, I just add one portion to a can of beans or lentils; cook for 15minutes and garnish with coriander.  

* Processed tomatoes have higher levels of lycopene, which is an antioxidant, in them.

All these ingredients can be found instore, alternatively, I can make up a package with the ingredients and exact measurements for this recipe