1. Preheat the oven to 350 degrees Fahrenheit (180 degrees). Spray a large bundt pan with non-stick spray and set aside for the time being.
2. Melt the butter, rum (if using), and the brown sugar in a small saucepan over a medium heat until it has formed a sauce, then set aside while you prepare the biscuits,
3. While the sauce is cooking, separate all the biscuits from each other, then cut each one into four pieces.
4. Combine the granulated sugar and the cinnamon in a gallon-sized zip-lock bag and shake until well mixed, then add in the biscuit pieces and seal the bag. Shake around until all the pieces are coated in the cinnamon-sugar.
5. Place all the biscuit pieces into the prepared bundt pan.
6. Pour the brown sugar-butter sauce over the biscuits in the pan.
7. Bake for 40-45 minutes until dark golden brown. Let it cool for 5 minutes, then flip it out of the pan onto a serving plate.