My favorite seasonal ingredient is pumpkin or winter squash.  In Chinese all winter squashes are called pumpkins so I am going to take the liberty of generalizing.  Pumpkin in particular can lead to come a rather amazing pumpkin roll, a recipe hailing from Castine, Maine, where pumpkin is duly revered. But once you have created a pumpkin pie you have the luxury of making a sweet potato pie and the associations roll on.  Why be limited to one ingredient?