All-Purpose Tomato Thokku/Pickle/Chutney | Side Dish for Idli Dosa

I had been recently trying to make jams and chutneys to preserve and to come in handy for that very-hungry-want-food-immediately days. After my successful attempt at the Dates and Figs jam, I made this Tomato thokku from Denny's site. This all-purpose thokku is a great side to idli/dosa/upma/Adai and also to bread/chapathi/parathas/rotis/curd rice. The below proportions lasted for a couple of weeks for me and I am making a batch again today as I am typing this. 
For my new readers, Denny of Oh Taste N See and I are college buddies who share the common interest of food blogging. I always wonder how she manages to cook up a storm every week. Yes, she has guests or friends over for lunch/dinner every weekend. If she is not having guests for a weekend, she goes to some potluck :). Do check out her space for a colorful treat!

Ingredients:
Yields about 2 cups of finished thokku
Crushed Tomatoes - less than 2 cups - I used half of a 28 oz can of organic crushed tomatoes (Check out what I made with the remaining half of the canned tomatoes here)
Onions - 2 cups - approx one big onion halved and thinly sliced
Garlic - 3 cloves - sliced thin
Gingelly oil - 2-3 tbsp (available in Indian grocery stores)
Mustard seeds - 1/2 tsp
Split Urad dal - 1/2 tsp
Turmeric powder - 1/4 tsp
Chilli powder - 1/2 - 3/4 tsp
Garam masala - 1/2 tsp
Lemon juice - 1 tbsp
Curry leaves - 1 sprig - optional - I didn't add
Salt - to taste

Method:
Heat oil in a wide non-stick pan over med-high heat. Add the mustard seeds, urad dal and curry leaves (if using). When the urad dhal changes color, add the sliced onion, garlic and a dash of salt. Cook till the onions turn soft and golden brown, stirring once in a while. Reduce the heat to medium and let the onions caramelize, about 5 minutes. Add the turmeric powder, chilli powder and garam masala and fry for a minute. Add the canned crushed tomatoes and salt to taste.
Allow the mixture to boil and check for salt/seasoning. Here comes the "be patient" part. Reduce the heat to med-low to allow the tomato to cook slowly (uncovered). Stir every 5 mins and cook for about 30 to 40 mins until all the water has evaporated and the chutney comes as one big mass and starts leaving the sides of the pan. At this stage the oil would start oozing out of the mixture. Add the lemon juice and fold to mix. Remove from heat and let it cool. When cool transfer it to a sterilized container. This can be stored in the fridge for weeks. Serve with idli/dosa/chapathi/bread/rice or anything you wish. As the name indicates this is an all-purpose side dish.
Note: Always use dry spoon when taking the chutney. Do not compromise on gingelly oil while making this chutney. It enhances the taste and acts as a natural preservative. If the canned tomatoes you use already has added salt, keep a check on the salt you add to the dish.