I'll fry up some pancetta, then take the grease and coat some rosemary and garlic then roast those.
In a pan bring heavy whipping cream to boil with whatever cheeses you want, rosemary, and roasted garlic to cream. Reduce to Alfredo consistency.
I always use reds, the texture of the skin and the inside of the potato is perfect for mashing (and roasting mah gawd)
Mash with heavy whipping cream, plenty of butter, cracked black pepper, add the pancetta during mashing. You want a grainy salt, kosher at the least. Himalayan pink salt is perfect.
Take the reserve rosemary, cheese Alfredo (cahills Irish porter cheese is beautiful for this) and use it as a sauce.
Garnish with fried rosemary sprig.