In heavy 12-inch skillet over medium heat on Wolf cooktop, heat oil. Add leek and coriander and cook about 6 minutes, until almost tender, stirring often. Add squash; sprinkle with salt and pepper and sauté until squash begins to soften, about 3 minutes. Add broth. Bring to boil, reduce heat to medium, and simmer uncovered about 10 minutes until vegetables are soft. In small batches puree soup in blender or food processor until smooth. Season with salt. Whisk crème fraîche and peel in small bowl. Divide soup among bowls, top with dollop of lemon crème fraîche. Serve warm.
*Sold at some supermarkets and at specialty foods stores.