Preheat your oven to 400°F (200°C).
On a lightly floured surface, gently roll out your thawed puff pastry into a rectangle, about 10x12 inches.
In a mixing bowl, combine the brown sugar and cinnamon. Spread the very soft butter evenly over the surface of the puff pastry, then sprinkle the brown sugar mixture generously over the buttered pastry.
Starting from one long edge, carefully roll the puff pastry into a tight log. Pinch the seams to seal.
Using a sharp knife, slice the log into 1-inch thick rolls. Place them cut side up on a baking sheet lined with parchment paper.
If desired, whisk the egg and lightly brush the tops of the rolls with the egg wash.
Bake the cinnamon rolls in the preheated oven for 15-20 minutes or until they are puffed and golden brown.
While the rolls are baking, whisk together the powdered sugar, maple syrup, melted butter, vanilla, and milk until smooth.
Once the rolls are out of the oven and slightly cooled, drizzle the glaze over the warm rolls. Serve immediately.