1. In a six- or eight-quart pot, sauté leek, zucchini, and potato in oil for 10 minutes, stirring occasionally.
2. Add the cauliflower, salt, and pepper and sauté another minute.
3. Add water just to cover vegetables and bring to a boil. Reduce to simmer and cook for 30 minutes.
4. Blend with an immersion blender until smooth. Top each bowl with caramelized pine nuts (see below), if desired.