Place undrained tomatoes, water, ginger, garlic, salt, turmeric, cayenne, and 1 teaspoon of garam masala into the heated blender container.
Press the Soup 2 button.
When the blender shows DONE, using a hot pad carefully remove the inner insert on the lid and set aside. Add the cubes of butter and 1 teaspoon of garam masala through the opening in the lid. Place a towel on top of the opening and press BLEND LOW.
Allow the blender to process the butter and soup for 10 seconds. Then, add 1/2 cup of cream in a slow steady stream.
Process for 10 seconds until the cream is well-incorporated into the sauce. Press CANCEL to turn off the blender.
Garnish with cilantro and serve.
Do not add your butter and cream until after your soup is done cooking, for best results.