Ok, I should probably not claim this to be "the" north Indian curry. But it is more or less what I've been learning in the kitchens of north Indian households. A lot of variations are available to this basic curry mixture. Mostly new spices are added to enhance the flavors.
1. Onions- 1 medium
2. Tomatoes- 2 medium sized
3. Garlic- 2-3 cloves
4. Green chilies-1-2 (depending on desired hotness)
5. Ginger (Adrak)-half inch piece
6. Oil or Ghee(clarified butter)-1 tbsp
7. Salt to taste
8. Turmeric powder (haldi)-1/4 tsp
9. Red chilly powder (lal mirch)-1/2 tsp
10. Coriander seeds powder (Dhaniya powder)-1 & 1/2 tsp
11. Garam masala (a spice mix, popular in North India)-1 tsp
1. Blend the onions and garlic together.
2. Blend tomatoes, green chilies and ginger. Keep aside.
3. Heat oil. Add the onion-garlic paste. Cook at high flame till the paste leaves the oil on the sides.
4. Add tomato paste and cook on medium flame. Add all the spices.
5. You may add a little water here if the paste is too thick to stir. Cook till small bubbles come to the surface and the mixture leaves oil on the sides.
6. The curry is ready.
Add your choice of precooked or semi-cooked vegetables here. I use it for boiled potatoes and peas to make aloo matar or mushroom with peas to make mushroon matar.
In a similar manner I make matar paneer (Peas with cottage cheese),though in the later stage of cooking, I add a little cream to sweeten it.