Preheat oven to 350F / 177 C and cover baking sheet with parchment paper. Place the rack in middle position.
Place the poppy seed mixture in a medium bowl and set aside.
Melt milk (or dark ) chocolate in microwave and mix it with poppy seed mixture. (Melt the chocolate on power 70% for 1 minute.)
On a clean surface, dust 1 tbsp of flour & roll out the puff pastry on of 15" x 12" rectangular shape. If you are using already pre- rolled sheet, just unroll it and spread the poppy seed mixture, leaving a 1/2 inch border uncovered. (If you have smaller size of puff pastry, use less filling.)
Tightly roll the dough into a log. Place the log on its seam. Using a sharp knife, cut the log in half lengthwise, but do not cut completely through. Then, the two sides needs to be twisted like a braid. Try to lightly twist and bring on the top the cut edge, so it creates beautiful swirls.
Brush off the babka with egg wash and bake it in the preheated oven for 40 minutes.
Let it cool down for 5-10 minutes and cut slices 1 inch wide. You can also sprinkle the babka with confectioner sugar if you wish!