Heat the oil in a pan and cook the diced onions over medium heat until very dark brown, stirring often. As she says in her comments, you are not after the mild onion flavor here. You want them BROWNed but not burned.

Meanwhile, put the ginger, garlic, chilies and water in a blender and process until smooth.

Once the onions are browned, add the ginger, garlic and chili mix and cook 3 minutes.

Add the cumin, turmeric, garam masala and cook for 2 more minutes, stirring.

Pop the can of tomatoes into the same blender and whir until blended. Dump this into the pan along with the salt, chopped cilantro and 1 cup (plus) water. Stir and simmer 15 minutes over low heat.

Take off the heat and let cool before freezing. This makes enough for 4 meals for 4-5 people so freeze according to your family size.

See http://mortgagefreeinthree.com/2012/05/curry-in-a-hurry/ for recipes on how to use.