Sweet Potato and Caramelized Onion Soup

Preheat oven to 350°. Brush potato halves with oil and sprinkle with salt. Arrange potatoes, cut sides down, on a baking sheet lined with parchment paper. Bake until very soft, about 45 minutes. Remove from oven and let cool. Scoop out flesh and set aside; discard skins.

In a large saucepan, melt butter over medium-low heat. Add onion; cook, covered, until tender, about 15 minutes, stirring occasionally. Uncover pan and cook, stirring occasionally, until golden, 3 to 5 minutes. Add ginger and garlic; cook for 1 minute. Add allspice, mace and nutmeg; cook for 1 minute. Add cooked sweet potato and stock.

Increase heat to medium-high and bring to a boil. Reduce heat and simmer, uncovered, until thickened, 45 to 60 minutes, stirring occasionally. Let cool slightly. Puree soup in batches in a blender or food processor. Season with salt and pepper. Serve with sour cream, if desired.