Saag Sauce

In a large pot, bring 2 inches of water to a boil. Add the spinach and cook, stirring often, until wilted, about 2 minutes. Drain and let cool. Transfer to a blender and puree until smooth. 

In a large skillet, heat the oil over medium. Add the cumin seeds. Once the oil splutters, add the onions and cook, stirring often, until slightly golden, about 5 minutes. Add the ginger and garlic and cook until fragrant, about 2 minutes. Add the tomato puree and spices and cook until the flavors meld, 5 to 6 minutes. 

Add the pureed spinach, the cream, and butter to the skillet. Stir until heated through; season with salt.