In a small bowl, combine the brown sugar and the cinnamon.
In a separate bowl, whisk together the eggs, milk and vanilla extract.
Spread a thin layer of pumpkin puree (as if you were buttering a piece of bread) on top of six slices of the bread.
Layer the 6 pieces of bread, pumpkin side up, into the baking dish on top of the melted butter.
Next, sprinkle half of the brown sugar and cinnamon mixture over the top of the pumpkin that is spread on the bread.
Now, spread a thin layer of pumpkin puree same as above on the remaining six pieces of bread.
Place each slice on top of the other slices making a sandwich AGAIN with pumpkin side UP.
Sprinkle again with the cinnamon/brown sugar mixture.
Pour the egg mixture over the top of all of it and then sprinkle more brown sugar and cinnamon over the top, if desired.
Cover and refrigerate overnight or at least 4 hours. Honestly, the longer the better.
When you're ready to serve, cover the dish with tinfoil and bake in a 350 degree oven for 30 minutes. Remove from oven, uncover the dish and bake an additional 15 more minutes. It should be golden and set.
Remove from oven and serve hot. Sprinkle with some powdered sugar if you want. This can also be served with syrup, butter, whipped cream or just eaten plain. It is delicious!