Indian Curry Gravy

1 cup rice bran oil
1.6 kg onions, chopped – use a food processor
1 kg fresh tomatoes, chopped (or substitute plain canned tomatoes)
5 green cardamom pods
10 black peppercorns
3 cloves
1 bay leaf
5 cm cinnamon stick
¼ cup garlic ginger paste
2 tsp turmeric
1 tbsp kashmiri chilli powder
1 tbsp cumin powder
2 tbsp coriander powder
1 tbsp SIDS SALT & PEPPER
4 green chillies, seeded
handful of coriander leaves
1 cup water

You need a lot of chopped onions for this. Do yourself a favour and use a food processor if you have one.
Peel and half the onions. Cut each half into six pieces. Fill your food processor about ⅔ full and pulse around 5-8 times. You should have diced onions. Repeat until you have chopped all the onions.
As long as your food processor is out, use it to chop the tomatoes. (if using fresh) Easy.
Heat the oil in a pot large enough to hold all the ingredients. Add the oil and heat over medium.
Once the oil starts to shimmer, add the cardamom, black peppercorns, cloves, cinnamon and bay leaf.
Let the spices bubble for about 20 seconds and then add the onions.
This takes some time and attention. Cook the onions over medium heat. Stir every minute or so. You want them brown. Nice and brown. Not tan - Brown. Think French onion soup. This is going to take around 30-40 minutes and maybe more. But you are doing it once. For 8 restaurant portions of curry. So it's under 5 minutes a curry. Totally worth it.
While the onions cook do the rest of the prep. Make sure the tomatoes are chopped. Cut the green chillies in half and seed them. (use a spoon)
Add the turmeric, cumin, coriander and kashmiri chilli powder in a bowl. Add about a ½ cup of water and stir to make a slurry. You may need to add a bit more water.
Once the onions are a nice creamy brown mess, add the garlic ginger paste. Stir to combine and continue to cook for about two minutes.
Add the powdered spice slurry and SIDS SALT & PEPPER. Cook another 3 minutes.
Add the chopped tomatoes, green chillies and coriander. Simmer until the tomatoes are broken down. This takes about 10 minutes. The oil may have separated at this point. If it did, do NOT remove it. It's pure flavour.
Add a cup of water. Let it cool a bit. Purée the curry gravy, whole spices and all. Yes. Whole spices get puréed. Use a blender. If it's too thick to purée, add a bit more water.
Make sure you vent your blender. Steam needs to escape or you'll be off to the hospital burn unit. Not good. Safety first.
You should now have about 8 cups of magic curry gravy to use in all sorts of curries.