Preheat oven to 375 degrees F.
Place sweet potatoes, 1/4 cup of the maple syrup, 2 tablespoons of the olive oil, 2 teaspoons salt and 1 teaspoon pepper in a large mixing bowl. Toss to evenly coat and place on sheet tray. Roast in the preheated oven for 35 to 40 minutes or until sweet potatoes are soft. Be sure to check on them after 15 minutes and stir, if needed.
Meanwhile, in a medium saucepan over medium-high heat, melt butter and add remaining 2 tablespoons of olive oil. Add the sliced onion, 2 tablespoons of maple syrup and season with salt and pepper, to taste. Saute until deep golden brown, about 2 minutes. Remove from the heat and set aside. Add water, 1 tablespoon at a time, if the pan becomes dry.
Transfer sweet potato mixture to a food processor, (may need to be done in batches) and add about a tablespoon of hot water. Pulse until just blended and then add half the caramelized onions. Pulse just a few times until desired consistency, adding more hot water for a smoother puree. Fold in remaining caramelized onions, reserving some for garnish.
Serve in a warm dish and garnish with the reserved caramelized onions. YUMMY!!!