These caramelised onion and blue cheese tarts are a delicious combination of sweet and savory flavors. The caramelised onions add a rich and sweet taste, while the blue cheese adds a tangy and creamy element. The tarts are made with a buttery pastry crust that complements the filling perfectly. They are perfect as an appetizer or as a light lunch option. Serve them warm or at room temperature for the best flavor.