1 pound Idaho potatoes, peeled and cut into 1-inch cubes
1 pound Yukon Gold potatoes or Yellow Fin, peeled and cut into 1-inch cubes
8 large garlic cloves, peeled
1 tablespoon salt (for cooking the potatoes)
1 1/4 cups heavy cream
1/2 cup unsalted butter, room temperature, cut into tablespoon portions
1/4 teaspoon freshly ground nutmeg
2 teaspoons sea salt for the pureed potatoes
1/2 teaspoon freshly ground white pepper
Place potatoes and garlic in a large casserole and add enough water to cover 2 inches above potatoes. Bring water to boil over high heat. Add 1 tablespoon of salt. Reduce heat to medium and cook potatoes until tender or easily pierced with the tip of a knife; 15 to 20 minutes.
Heat cream in a small saucepan over high heat until bubbles start to form around edges. Keep warm, but do not boil.
Drain potato/garlic mixture; return to pan and dry potatoes over medium heat for one minute to remove excess water. Immediately run the potato/garlic mixture through a food mill and place in a mixing bowl. Or, place the mixture in the bowl of an electric mixer and beat on medium speed until lump-free.
Add cream gradually, mixing on medium speed, scraping bowl occasionally. Add enough cream to give potatoes a soft-mounded consistency, similar to softly whipped cream. Mix in butter, a few tablespoons at a time. Add nutmeg, salt and white pepper; beat until well-blended.