In a 3 quart sauce pan, heat the olive oil and butter over medium heat. Add the onion, garlic, and ginger, reduce the heat to medium and sauté for about 10 minutes, or until onion is starting to turn golden.
Add the garam masala, cumin, coriander, and sauté for 2 minutes. Stir in the spinach, salt, and 1/2 cup water, turn the heat to low and cover. Cook for 3 minutes or until spinach is warm.
Turn the heat off, stir in the yogurt and heavy cream. With an immersion blender, blend the mixture to a smooth pureé.