In a small bowl, combine the brown sugar and pumpkin pie spice. Remove 1/4th cup for later.
In a medium bowl, mix the butter, 1/4th cup pumpkin and flour together. It's okay if some of the butter clumps.
Once the dough has rested, cut dough into two halves.
Sprinkle clean surface lightly with flour and roll out the first half of dough until it measure around 15 x 9. Spread the softened butter mixture over the dough and dust evenly with half the cinnamon sugar mixture. Roll the dough up tightly and cut into 7 even rolls.
Place the rolls into the prepared pan. Repeat with the second half of dough, but make sure to leave space in between the rolls. Once all the rolls are in the pan, cover with aluminum foil. Place in the heated oven, turn off heat and let them rise for 20 minutes.
In the meantime, make the cream mixture. In a small saucepan, add the heavy cream, 1/4th cup pumpkin puree, egg and remaining 1/4 cup pumpkin pie spice mixture from earlier. Whisk on low heat until completely combined and warm but not hot.
Once rolls have rested, remove the foil and stream the heavy cream mixture over the top of the buns. Return the rolls to the oven and turn on the oven to 375ºF. No need to pre-heat the oven. Bake for 20-25 minutes until the top of the buns are golden brown.