This soup is clean and light yet packed with flavor thanks to umami-rich miso. Sriracha (or chili-garlic sauce) adds garlicky notes as well as spiciness and a little tang; use the smaller amount for mild palates or the larger amount (or even more) for those who like a little burn. We prefer lacinato kale (also called Tuscan kale or dinosaur kale) over curly kale in the soup, as lacinato’s texture is silkier and more tender, but either type works. You also can use tofu of any firmness, from silken to extra-firm, but if using the softer types, be sure to stir gently to avoid breaking up the pieces.