Preheat the oven to 400˚F. Line a baking tray with silpat or parchment paper.
Combine the egg yolk with a touch of water just to loosen it up.
If you cannot buy pre-rolled puff pastry sheets, roll out your puff pastry on a floured surface until you have a rectangle that is approximately 10×12 inches. Using a pastry brush, egg wash the first sheet of puff. Sprinkle with the chocolate chips so the sheet is covered. Top with the second puff pastry sheet and pat down gently so the chocolate chips stay put. Coat with egg wash.
Roll up the long side of your sandwiched sheets. Gently elongate the rolled puff pastry using your hands, taking care to keep the seam in place so chocolate chips do not drop out. With the rolled puff vertically oriented in front of you, leave an inch at the top and then cut vertically through the roll until you reach the bottom. Twist each end and shape into a big heart, crossing the ends over each other to close the heart at the top. Egg wash again and bake in the oven for 15-20 minutes or until the puff pastry is completely cooked through.
Enjoy this while still warm!