Fill a large pot about halfway with cold water. Peel the sweet potatoes and cut them into a medium-dice, doing your best to have them be similar-sized pieces. Place the diced potatoes into the pot of water. Swirl the potatoes around in the water, then drain.
Pour fresh cold water into the pot until the potatoes are covered. Place the pot on the stove, cover, and turn the burner to high heat. Bring to a boil. Reduce to medium-high heat, and continue cooking with the lid on the pot, stirring occasionally, until the potatoes are fork tender, about 25-30 minutes.
While the potatoes are simmering, add the butter and milk to a small saucepan over low heat. Cook just until the butter has melted. Take off the heat and set aside.
Drain the potatoes and return the potatoes to the hot pot. Let them sit with the lid off for 5 minutes, so the excess steam can escape. Pour the butter and milk mixture into the pot and mash the potatoes with a potato masher until smooth.
Add the sour cream and stir it in. Then add the salt, pepper, garlic powder, and onion powder, and mix. Taste and adjust the seasoning as needed.
When you are ready to serve, stir in the parsley, chives, and thyme. Serve immediately with more butter and herbs for garnish, if desired.
Notes
Store leftovers in the fridge for 5 days in an airtight container. Freeze for up to 3 months.
If you want to bring back some of that sweetness out of the potatoes, you absolutely can. Add a tablespoon or two of maple syrup, honey, or brown sugar, taste adjust to your palate. I would not add too much additional sweetness, though, because this isn’t supposed to be a sweet side. Just a hint would be a nice addition.
Some other seasonings that would be good: creole seasoning, blackening seasoning, bbq seasoning, or a pinch of nutmeg. If you are going to add a seasoning mix, I would add less salt since they normally have salt added.