While the dough is resting, make the filling. In a medium bowl, mix together the brown sugar, granulated sugar and cinnamon. Set aside.
Line the slow cooker with parchment paper and slightly spray the parchment with cooking spay or brush with oil. *If baking in the morning, skip this step until you're ready to bake.
After the dough has rested for at least 10 minutes, roll it out into a 14x8 inch rectangle.
Using an offset spatula, spread the softened butter onto the dough, leaving a border all around the edges.
Sprinkle the cinnamon sugar mixture on top of the butter.
Starting from one of the longest sides, tightly roll the dough into a log.
Using a serrated knife or dental floss, cut the dough into 10-12 even pieces. *Instructions below on how to prepare the night before and bake in the morning.
Place the rolls into the lined slow cooker.
Warm the heavy cream in the microwave until lukewarm, about 15-20 seconds. Add the vanilla and stir to combine. Gently pour the cream over the rolls in the slow cooker.
Place a piece of paper towel under the lid to absorb excess moisture. Do not skip this!
Turn the slow cooker on to high and allow to cook for 1 hour. After 1 hour, turn to low and cook for 1 hour. Each slow cooker seems to have different temperatures, so check on the rolls after about an hour and a half to gauge their doneness
Once they’re done, remove the rolls from the slow cooker immediately by lifting them out with the parchment paper.
Set aside to cool slightly.