I start a curry by frying up loads and loads of onions (3 whole ones, coarsely chopped) for at least 20 minutes on a low heat in oil or ghee (clarified butter) then I add the spices - turmeric, fresh chopped chilli (or you could use ground chilli powder), cumin seed, ground coriander, 3 or 4 cloves of chopped garlic and a little salt) and fry them in the oil and onion mix for just a couple of minutes. I then add a couple of tablespoons of concentrated tomato puree, fry for another couple of minutes and then add a mugful of water and stir well. I cook it all until the water has evaporated and I am left with a red onion paste in oil. I then add my curry ingredients, eg potatoes, mushrooms, whatever, fry for a few minutes, then add more water, stir well and let it simmer until the veg is cooked.
If you want more exact quantities, just let me know !