Heat oven to 350°. Prepare a 8x8 baking dish and spray with cooking spray. Set aside.
Cut each biscuit (8 total biscuits in tube) in half and then cut each half into 3 smaller pieces. So each biscuit should end up being in 6 small pieces. Repeat with remaining biscuits.
Add biscuit pieces into a mixing bowl. Add the brown sugar and ground cinnamon and stir together until all the biscuit are coated. It's ok if there is some sugar mixture left in the bottom of the bowl.
Pour the coated biscuit pieces into the baking dish. You can either sprinkle the remaining sugar mixture over the biscuits or discard it. Make sure that the biscuit pieces are in a single layer and that they are not overlapping or on top of each other.
Drizzle the melted butter evenly over the biscuits.
Cook for 20-23 minutes or until the biscuits are done.
While the casserole is cooling for a few minutes, prepare the vanilla glaze by combining everything together in a bowl and whisking together until smooth and combined. Drizzle or pour over the cinnamon roll casserole. If you want a pretty presentation, pour the glaze into a Ziploc bag and cut a small corner off of the bag, then drizzle the glaze over the casserole.
This is best eaten within an hour of making it. If there are leftovers, I would warm it up in the microwave for a few seconds before eating it.