Mix pork, onion,spring onion,five spice powder,fish sauce,rice wine,corn flour and water in a bowl. Stir until all of the ingredients have combined.
Cut the pastry sheet into 3-inch squares.Place about 2 tablespoon pork mixture in the middle of each square. Fold squares over the filling to form triangles. Brush with a little of the egg yolk and sprinkle with sesame seeds.
Set the oven to 200 degree and bake for 20 minutes or until the pastry is golden and crispy.