Once the dough has doubled in volume, punch it down gently.
Grease the baking tray liberally with oil and place the dough on the pan and flatten ti until it spreads out to all the sides. Spread the dough evenly to ensure that they bake evenly.
Cover the pan and let the dough rest for about 30 minutes.
In the meantime, preheat the oven to 425 F.
Once the dough has rested, make dimples with your fingers all over the dough.
Evenly spread the caramelized onion and then sprinkle the poppy seeds.
Bake for about 20 minutes until the Pletzel is evenly browned.
Remove from the oven and let it cool a bit. Slice it into pieces and serve.