Melt butter with oil in a large saucepan over high heat; add shallots and next 2 ingredients; sauté 2 minutes. Add curry powder and next 5 ingredients; cook, stirring constantly, 1 minute. Stir in tomato paste; cook, stirring constantly, 30 seconds. Stir in potatoes. Reduce heat to medium. Cover and cook, stirring occasionally, 5 minutes. Add broth and cauliflower. Increase heat to high; bring to a boil. Cover partially, reduce heat to medium-low, and simmer 6 minutes or until potatoes are tender. Reduce heat to low. Meanwhile, whisk together cornstarch and 2 Tbsp. cold water in a small bowl until smooth. Whisk into buttermilk. Slowly stir buttermilk mixture into vegetable mixture, and cook, stirring occasionally, 2 to 3 minutes or until mixture begins to simmer. Stir in spinach in batches, and cook 2 to 3 minutes or until wilted. Remove from heat, and serve immediately over rice.
This recipe is okay. Not a lot of flavor in the curry. I added extra hoping it would be spicy, however, the buttermilk really tempers any heat.