Bread pudding is a way to repurpose stale bread, soaking it in a custard (typically made of milk or cream and eggs) and baking it into a soft, flavorful side dish, or dessert. Its history goes way ...
Since pumpkin pie is basically a custard on top of a crust, an easy way to cut down added sugar and carbohydrates is to make a crustless version. Think of it like a creme brulee (minus the brulee).