The recipe for a basic curry sauce is as follows:
-2 tablespoons peanut oil
-1 tablespoon margarine or butter
-1 large onion, diced
-1 tablespoon minced fresh ginger
-1 teaspoon each of cinnamon, black pepper, and cayenne pepper
-2 tablespoons each of ground coriander and cumin
-1/4 teaspoon ground turmeric
-1 large can of diced tomatoes
-2 Serrano peppers, seeded
-about 3 cups water
-1/2 cup plain yogurt
Directions: Heat the oil in a pan over medium-high heat and saute the onions until translucent. Add in the garlic and ginger and saute for an additional 2 mins. Remove from pan and process in a food processor or blender until smooth. Place this mixture back into the pan and add in the other spices and cook until thickened into a paste-like consistency. Using the blender or processor again, puree the tomatoes and peppers until smooth. Add into the pan with the onion and spice mixture over low heat. Slowly add in a bit of the yogurt at a time, stirring to avoid curdling. If you want the sauce very smooth, you can place this mixture back into the blender and blend further. Otherwise, add in 3 cups water, bring everything to a boil, then reduce heat and cover and allow to simmer 3-5 minutes or until it reaches your desired consistency.
This is a basic, base recipe and can be customized with other ingredients to change the flavor. Ie, using coconut milk for a coconut curry. I hope this helps!