I begin by placing heavy cream, whole garlic cloves, and rosemary sprigs into a small saucepan. I gently bring it to a simmer and then lower the heat. I let it steep slowly for about an hour so the garlic softens and aromatics infuse the cream.
While the cream is infusing, I peel and cube the potatoes, then put them in a large pot with chicken stock (or salted water). I bring it up to a boil and cook until they’re easily pierced with a fork—around 15–20 minutes depending on the size of chunks.
After draining, I return the potatoes to the pot (on low heat to evaporate excess moisture). I discard the rosemary sprigs, then pour in the infused cream and melted butter. I mash gently until the lumps are gone. Finally, I transfer to a bowl or mixer and whip for about a minute, then season with salt and white pepper to taste.