In a large soup pot, brown Italian sausage and break it up with a wooden spoon. After sausage is brown (about 8 minutes), add in garlic and onions. Stir and cook until onions are translucent.
Add sliced potatoes, chicken stock, water, and salt. Cover and simmer for 10 minutes.
Stir and add in kale and simmer for another 15 minutes, or until the potatoes are fork tender. Add in milk, and red pepper flakes. Stir and serve.