Bring water to a boil in a small saucepan, add the garlic cloves, and blanch for 2 minutes.
In a 4-quart casserole melt the butter with the oil over medium heat. Add the stock, kale, diced potatoes, and blanched garlic cloves and season with salt and pepper. Bring to a boil, reduce the heat, partially cover, and simmer for 25 to 30 minutes or until the vegetables are tender.
With a slotted spoon, remove about 2 cups of vegetables from the broth, excluding the garlic cloves, and reserve. Strain the soup into a large bowl. Transfer the drained vegetables to the work bowl of a food processor or blender and process until smooth.
Whisk the pureed vegetables into the strained broth and return to the casserole. Add the reserved 2 cups of cooked vegetables and the optional heavy cream. Bring to a boil, reduce the heat, and simmer for 10 minutes. Taste and correct the seasoning and serve hot, accompanied by a crusty loaf of French bread.
MEYERS, Perla - Perla Meyers' Art of Seasonal Cooking