Prepare puffs through step 4. Prepare filling in step 5; spoon into 2 pastry bags, each fitted with medium round tip.
Using chopstick or skewer, poke a hole in bottom of each puff. Pipe in the filling through holes.
Swirl sugar and water in medium-size saucepan over high heat until mixture is clear and the sugar is dissolved. Reduce heat to medium and cook, swirling mixture in pan occasionally, 25 to 30 minutes, until golden and fluid. Handle caramel very carefully, as it is extremely hot. Remove from heat; let cool slightly.
Line baking pan with foil. Using a fork, dip top halves of filled puffs into caramel, allowing excess to drip back into pan. Transfer to foil-lined sheet. Continue with remaining puffs and caramel, reheating caramel when necessary if it becomes too stiff.
Once puffs are dipped in caramel, begin sticking together in a ring on the serving dish. You may need to re-dip tops of puffs in caramel to get them to stick together. First layer should use 8 large puffs. Continue stacking filled and dipped puffs, using smaller sizes as the tower gets higher.