This Sweet Potato Spinach & Caramelized Onion Tart is a delicious and flavorful dish that combines the sweetness of roasted sweet potatoes with the earthiness of spinach and the rich flavor of caramelized onions. The tart is topped with a tangy balsamic reduction, which adds a burst of acidity and complements the other flavors perfectly. It's a great option for a vegetarian main course or a side dish for a special occasion.