In a sizable stockpot or Dutch oven, set over a medium-high flame, proceed to brown the Italian sausage until it crumbles appropriately. Utilizing a slotted spoon, extract the sausage and ensure the pot is free from excessive drippings.

Subsequently, reintroduce the browned sausage to the pot. Incorporate the diced Russet potatoes, chicken stock, ½ teaspoon of kosher salt, and ¼ teaspoon of freshly ground black pepper. Allow the mixture to reach a boiling point before reducing the heat to medium. Maintain the cooking process until the potatoes have achieved a tender state, which should typically span approximately 10-12 minutes.

Using the aforementioned slotted spoon, extract precisely half of the potatoes from the pot. In an isolated vessel, thoroughly mash these potatoes. Once this task is accomplished, return the mashed potatoes to the primary pot. Following this, amalgamate the chopped kale or spinach, heavy cream, and adjust the seasoning (salt and pepper) according to one's palate. Persist with the cooking until the kale or spinach exhibits a tender consistency, likely within 2-3 minutes.

Upon serving, each portion should be appropriately garnished with a generous amount of shredded parmesan cheese, an additional sprinkle of freshly ground black pepper, and a modest drizzle of extra virgin olive oil.