You can use also use a blender or even just an electric mixer to whip this up.
1.5 kg sweet potatoes, peeled and cut into chunks
6 garlic cloves, peeled
1/4 cup melted butter, divided
1/3 cup maple syrup, divided
1 1/2 tsp salt
1/4 tsp black pepper
Preheat the oven to 400°F (200°C). Grease an 8 cup (2 L) casserole dish.
Combine the sweet potatoes and whole garlic cloves in a roasting pan. Cover the pan tightly with foil (or a lid) and bake for 45 minutes to 1 hour, or until the sweet potatoes and garlic are very tender. Transfer to a food processor.
In a small bowl, stir together 2 tbsp (30 mL) of the melted butter and 1 tbsp (15 mL) of the maple syrup. Set aside. Add the remaining butter, maple syrup, salt and pepper to the sweet potatoes in the food processor. Process until puréed. Transfer to the prepared casserole dish, smooth the top and drizzle with the reserved butter and maple syrup mixture. Bake for 30 to 35 minutes or until the top begins to brown lightly.
You can make this ahead of time, but bake just before serving. Refrigerate the casserole, covered, and bring to room temperature before baking.