Heat the oil to medium in a stock pot or Dutch oven. Add the onion and sauté 4-5 minutes. Stir in the Italian sausage and sauté another 5-6 minutes, breaking up the sausage with a wooden spoon as it cooks. Stir in the garlic and kale and cook another 2-3 minutes, until kale has wilted. Stir in the potatoes, Italian seasoning, salt, black pepper, and red pepper flakes.
Add the stock and bring to a simmer for about 10-15 minutes, stirring occasionally, until potatoes are al dente. Stir in the evaporated milk and cook an additional 3-5 minutes. Taste and adjust seasoning, if necessary.
