Place the potatoes in a medium-sized microwave-safe dish in a thin layer. Microwave it on high heat until you can easily puncture your potatoes with a fork (about 7-10 minutes).
Immediately smash the heated potatoes in the microwave-safe dish using a potato masher.
Decant the half-and-half over your potatoes and top with a dab of butter. Put the potatoes back in your microwave for about 1 minute to reheat. To mix, stir everything together thoroughly. Come back to the microwave for another 1 minute. Sprinkle it with salt to taste.
Cover firmly with the plastic wrap and keep inside your refrigerator for almost a day if made ahead. Microwave on high heat for 30 seconds until it's well warmed. Then, garnish with chives if desired.