Heat the olive oil in a stock pot over medium heat. Add the sausage and break it apart with a wooden spoon. Allow the sausage to brown, stirring frequently, for 7-10 minutes. Remove the sausage from the pan with a slotted spoon and set aside.
Add the butter to the pot and let it melt. Slowly whisk in the flour until the mixture is smooth and bubbly.
Add the onion, fennel seeds, oregano, black pepper and a pinch of red pepper flakes and stir to coat evenly. Continue to cook until the onion begins to soften (approx. 5-7 minutes). Add the garlic and cook for an additional 30 seconds.
Slowly pour in the water and milk. Add the bouillon and stir until it is combined. Add the potatoes to the pot, cover and bring to a boil. Once it has reached a boil, remove the lid and lower the heat. Simmer, uncovered, until the potatoes are fork tender (approx. 10 minutes).
Add the kale and most of the cooked sausage back to the pot and cook for an additional 5 minutes.
Serve the soup topped with more black pepper, red pepper flakes and the leftover sausage pieces. You can serve this with some crusty bread for dunking.