Pumpkin and squash pies are simply a sweet starchy vegetable blended with a custard base (eggs and milk/cream). Sweet potatoes are a sweet starchy veg, Simply prep potatoes as you would pumpkin (roasted preferred as you get a degree of caramelization that deepens flavour) and puree and use them as pumpkin. Or google sweet potato pie - it's a southern US thing (has a bit more butter). I used Japanese sweet potatoes, which I like (and more importantly had on hand), but are white fleshed not orange fleshed, so I added a bit of food colouring and a bit of molasses to get a more pumpkin like appearance.
