Slice off top 1/2" of garlic head and wrap in tin foil.
Place potatoes and garlic directly on the middle rack, or baking sheet, for 30-40 minutes or until soft; a fork should go in with almost no resistance. (It is better to overcook than to undercook.)
While potatoes are cooking heat heavy cream and butter in a sauce pan. Keep below a simmer.
Using kitchen twine tie together sprigs of rosemary and add to sauce pan.
Once butter and cream are combined and just under a simmer, turn off heat and steep rosemary for 5 minutes.
Remove potatoes and garlic from oven and while still hot, with an oven mitt or tongs, cut potatoes in half and scoop out the potato from the skins.
Mash the potato with a hand masher or a ricer. Stand/hand mixer options are not required.
Pour hot butter and cream mixture into mashed potatoes and fold in mixture with a spatula until combined. No chunks should remain.
Add the salt. Taste and adjust as needed.
Garish with chives and freshly cracked black pepper.