Clean, peel & cut sweet potatoes into cubes. Place potatoes in a pot. Add enough water to cover the potatoes (above 1"). Optional: add a pinch of salt to the pot.
Bring the pot to a boil (uncovered). Then turn down the heat to medium and cook for 20-30 minutes or until the potatoes are fork tender.
Drain potatoes. Place in a bowl. Add butter, salt & garlic then smash with a potato masher. Add milk & sour cream. Smash until smooth.
Season with salt, cinnamon or black pepper if you prefer.