Preheat your oven to 400°F and line a 10” x 15” baking sheet with parchment paper.
Take a sheet of pastry dough, cut into four equally sized squares, and place on your baking sheet.
Prick holes in the center of the puff pastry squares, leaving 1 inch borders untouched.
Make a circular nest of onions in each square, leaving the 1 inch border so the puff pastry can rise to form an edge and space in the center for the egg to nestle into.
Brush the borders of the squares with the egg wash and place the baking sheet in the middle rack of the oven for 10 minutes or until the puff pastry border has risen like a wall around the onions.
Take squares out of the oven. Carefully crack one egg in a small bowl. Use your hand or a spoon to gently separate the egg yolk from the white and and nestle the yolk in the center of the onion nest. Slowly pour the egg white into your pastry square, leaving behind some of the white if you think it will overflow.
Season eggs with a sprinkle of salt on each egg. Repeat for the other three pastries.
Carefully place the pastries with the eggs back in the oven and cook until the eggs are cooked to your liking. For a runny egg it can take between 5-7 minutes but continue to monitor the eggs every 2-3 minutes and rotate your baking pan halfway through for even cooking of your eggs.
Remove the tarts from the oven and sprinkle the 4 green onions and fresh herbs on top. Enjoy!