In a large pot or dutch oven, add the sausage. Heat over medium heat and cook until browned and cooked through. Remove the sausage with a slotted spoon and transfer to a plate, leaving the fat behind. Add the oil to the pan only if you find there is not enough fat left over from the sausage. Add the onion, carrots and celery. Cook until the veggies are tender, about 7-8 minutes. Pour in the chicken broth and add the cubed potatoes. Season generously with salt, black pepper and Italian seasoning. Bring the soup to a boil and then reduce to a heavy simmer. Cook until the potatoes are tender, about 20 minutes. Add roasted garlic cloves to the pot. Turn the heat off and discard the bay leaf. With your immersion blender (alternatively you may use a regular blender - see below), blend the soup until about half of the soup is pureed. You will still want some larger chunks of potato and veggies remaining. Turn the heat back on to medium and add the already-cooked sausage, half and half (or substitute) and the kale. Cook until the kale is wilted substantially, about 6 minutes. Adjust the seasoning to taste and remove from heat.