Peel and dice the sweet potatoes and then blanch in boiling water for 3 minutes, until just tender. Preheat skillet or griddle to medium-high. Dice the bacon and render in the skillet until almost crisp, then pour off excess bacon fat. Add butter to the skillet. In a small mixing bowl, combine diced sweet potatoes, onion, rendered bacon, sugar, pecans, and scallions. Add sweet potato mixture to hot skillet and cook over medium-high heat. Toss or turn with a spatula frequently. To caramelize, let sit 2-3 minutes, without turning, just before serving. Season with kosher salt and fresh-cracked black pepper.