The people at the Today show, along with their partners at How Does It Grow, a non-profit food education website, have it covered. It turns out that the original pumpkin pie was much more pumpkin than pie.
According to the How Does It Grow video, the English settlers' version was a spiced custard baked in a pumpkin. Dating back to the original Harvest Festival dinners, pilgrims would scoop out the insides of what we now call a "pie pumpkin." Then, it would be roasted. After the pumpkin was cooked, it would be filled with a custard and cooked again until the custard was set.
Ready to do a Thanksgiving #TBT with your favorite dessert? Follow-up question: Can we come over?