Place peeled, cubed potatoes into a large pot of cold, salted water. Bring to a boil, then reduce heat and simmer until tender, about 15 minutes.

While potatoes cook, place beef sausage links in a skillet over medium heat. Roast until browned and cooked through, about 10-12 minutes. Set aside and slice.

In a separate small saucepan, combine heavy cream, crushed garlic, and half of the rosemary. Heat gently until simmering, then remove from heat to infuse.

Drain the boiled potatoes well and return them to the warm pot for 1 minute to evaporate excess moisture. Pass the potatoes through a potato ricer or mash thoroughly.

Strain the garlic and herb-infused cream into the mashed potatoes. Gently fold in the cream.

Fold the cubed cold butter into the potato mixture until silky and fluffy. Season with salt and pepper.

Serve the creamy mashed potatoes topped with the roasted beef sausage. Garnish with remaining rosemary and fresh parsley.