Combine spices in bowl. In med suacepan, heat butter, oil. Add leeks, onion; cook about 8 minutes. Sprinkle with spices; add sweet potatoes, squash, and carrots. Stir well to combine.

Add chicken stock to mixture, simmer over low heat, partially covered, until vegetables are tender, about 40 minutes. Season with salt and pepper. Remove from heat.

Transfer soup in batches to blender. Process until smooth.