Whether you make a creamy kale soup by blending it or make a traditional kale soup, you'll still be able to taste the leafy green vegetable's earthy, somewhat bitter flavor. When buying kale, choose bunches with the darkest green and freshest-looking leaves that don't have any yellowing at the edges. The Environmental Working Group, a nonprofit environmental research group, recommends that you buy organic kale to avoid high levels of toxic pesticides.
Kale stays fresh wrapped in plastic in your refrigerator for 3 to 5 days. When you're ready to cook, wash each leaf thoroughly under running water. Remove the fleshy part of the leaves from the stalks, or ribs, by pulling them off by hand, section by section, leaving the main stalk and the thick lower branching stalks intact. Chop the leaves roughly into large chunks if you plan to make a cream soup and into smaller 1-inch pieces for other soups.
Creamy Kale Soup
For depths of flavor in your soup, cook chopped onions and minced garlic directly in the soup pot. Add 2 cups of chicken or vegetable stock for each 2 to 3 cups of cut kale -- exact proportions aren't necessary in most soup recipes. Let the kale cook at a low simmer until it is soft and tender, about 10 minutes.
Pour the mixture into a blender and process, first at low speed and then on a higher speed, until the soup is smooth and creamy. Return the mix to the cooking pot, add 1 cup of milk for each 2 cups of stock and reheat the soup slowly. Squeeze a bit of lemon over each serving and garnish the soup with a dollop of sour cream.
Traditional Kale Soup
Kale soup from Tuscany, Italy, begins with sauteed aromatic vegetables, but adds 2 tablespoons of tomato paste for each quart of stock. It also contains cannellini beans, 4 cups of chopped kale for each quart of broth and sweet or hot Italian sausage. A bit of cider vinegar brings the flavors to life when it's stirred in just before serving.
Portuguese kale soup is similar, with Portuguese hot sausage, or linguica, diced potatoes and either cannellini or red kidney beans, all simmered, with an optional ham hock, until all the vegetables are tender.
Kale as a Secondary Ingredient
Even without a recipe, you can add chopped kale to just about any soup. Use a handful or 2 of chopped kale in place of spinach in minestrone, black-eyed pea soup, lentil soup or an Asian-inspired soup with pork, soy sauce and red bell peppers. Or, give your creamy potato soup or sweet potato soup a bit more color, texture and flavor with chopped kale cooked into the mix.