Heat a large nonstick skillet over medium-high heat. Add the olive oil. Add the sausage, breaking it up with the back of a wooden spoon, and cook until browned, 4 to 5 minutes. Add the red onions, fennel, garlic, thyme, salt, and pepper. Continue to cook, stirring frequently, for about 4 minutes, or until the veggies wilt and the onions become translucent. While the veggies are cooking, start the polenta.
In a sauce pot combine 2 1/2 cups of the chicken stock and 1 cup of milk. Season the liquid with salt and pepper. Place over medium-high heat and bring up to a simmer.
Once the veggies have wilted, add the white wine and the remaining 1 1/2 cups of chicken stock to the skillet. Turn the heat to high and bring up to a simmer. Cook to reduce the liquids by half, about 4 to 5 minutes. Stir in the chopped parsley.
To the simmering chicken stock and milk add the polenta and whisk completely until the cornmeal masses together. It's so cool how fast this happens--right before your eyes! Add the butter and grated cheese, stirring to combine. Keep in mind that polenta is very forgiving; if it becomes too thick, you can always add more warm chicken stock or milk.
Serve the polenta in a shallow bowl and top with a helping of the sausage and fennel ragout. Garnish with more grated parmesan.