Heat the olive oil in a wide based pot or Dutch oven
over medium heat. Add the onion, carrot, celery, garlic and chili flakes and cook 7-8 minutes, stirring occasionally, until partially softened. Season the vegetables with salt and pepper. Add the tomato paste and cook another 1-2 minutes until fragrant. Stir in the kale and cook until it starts to wilt, 3-4 minutes. Add the diced tomatoes, stock (or water), thyme, bay leaf and parmesan rind and raise the heat to bring to a simmer.