Heat oil in a shallow pan to medium low. Add oil and the dry spices. Wait until the spices are fragrant and your kitchen smells like a Bazaar from an exotic land.(about 1 minute)
Add ginger, garlic and let them soften (about 2-3 minutes). The important part at this step is to NOT burn the garlic.
Add the chopped onion and tomatoes and coriander leaves, let them cook until they marry each other. (Like successful marriages, this is an investment of time and patience). So cover the pan and let everyone greet each other for about 8-10 minutes. Keep checking though. At no point should your pan look like a burnt forest.
Turn off the heat. Let the yumminess in the pan cool. Puree in a blender or food processor along with the cream. Add salt, sugar and adjust to taste. When working with salt, remember you can always add more so start low.