Place the cubed sweet potatoes in a large pot or Dutch oven and add enough water to cover by about 1 inch. Add 1/2 teaspoon of the salt and bring the mixture to a simmer over medium-high heat. Reduce the heat and simmer, uncovered, until the potatoes are fork-tender, about 9 to 12 minutes.
Drain well, then return the potatoes to the pot. Mash the sweet potatoes to your desired consistency.
Add the most of the green onions and bacon - reserving a little for garnish if desired, and the garlic. Stir to combine. Next, stir in the sour cream, all of the butter, and the remaining 1/2 teaspoon of salt and pepper. Taste and season with additional salt and pepper if desired.
Transfer to a serving bowl and top with additional green onions and bacon, if desired. Serve immediately or store in an air-tight container for up to 3 days. If storing, wait to add garnishes until serving.