Heat the olive oil in a large saucepan or Dutch oven set over medium heat. Add the onion, celery and carrot, and cook until the vegetables begin to soften, about 5 minutes.
Stir in the garlic, rosemary, thyme, red pepper flakes and pepper, and cook for 1 minute.
Stir in the tomato paste and cook for 1 minute.
Add the potatoes and vegetable broth, and bring to a boil over medium-high heat. Decrease heat slightly and cook at a lively simmer for 15 minutes.
Add the beans and cook until the potatoes are tender, 10 to 15 minutes.
Stir in the kale and cook until just wilted, about 1 minute. Season with salt. Serve.