Heat up the oil in a frying pan. Fry the onions with a pinch of salt until they are golden.
Add the ground beef and mix for 5 minutes while breaking the meat chunks.
Add in the mushrooms, mix well and season right away. Sauté everything for 5 more minutes, then transfer to a bowl and let the mixture cool off.
Preheat the oven to 340 °F (170 °C).
Place the puff pastry sheet on a plastic wrap. Arrange the filling mixture across one end of each sheet as shown in the video. Roll the sheet inwards and tighten after each time you roll.
Place the rolled pastry sheets on a sheet pan lined up with parchment paper. Make diagonal cuts on each roll, then brush with the egg and sprinkle sesame seeds.
Bake for 20-25 minutes, or until the rolled pastries are golden. Remove from the oven and let it rest for 10 minutes.