Butter the bottom and sides of a 9 X 13 dish, and set aside.
In a large bowl, tear the croissants in bite size pieces.
In a separate bowl, combine the brown sugar, sugar, salt cinnamon, pumpkin pie spice, and baking powder, and stir well.
In another bowl, break the eggs, and beat them with a whisk until they're a light lemon yellow. Add the pumpkin, half n half and Vanilla, and stir well to blend.
Add the Sugar/spice mixture to the egg/pumpkin mixture and stir well.
Place the croissants in the buttered 9 X 13 dish, and pour the pumpkin mixture over the croissant pieces.
Dot the top of the dish with the butter cubes, and place the dish in a 400 degree oven for 40 - 45 minutes, or until the bread pudding is golden brown, and springs back when touched.
When the dish is completely baked through, remove from the oven, and allow to cool and set for at least 30 minutes.
When cooled a bit, cut into pieces, and serve. Enjoy!