Sift the flour, baking powder and salt to aerate the mixture. Keep aside.
Take the sugar and butter in a second bowl, use a hand-blender on medium speed to cream together until fluffy.
Add one egg, orange zest and vanilla extract, mix till well incorporated.
Slowly add the dry mixture to the wet batter, mix until just combined.
The dough should be crumbly in texture, do not overwork the dough. If the dough feels a bit too dry, add 2-3 tsp of cold milk, 1 tsp at a time, knead very lightly.
Wrap the cookie dough tightly in a cling film, refrigerate, at least 2 hours. (Overnight works best)
Pre-heat the oven to 180C.
Take the cookie dough out of the refrigerator, allow to come to room temperature.
Roll the dough over a well-floured surface to about 1/4th inch thickness. Using a 4-inch circle cookie-cutter, cut as many circles you can .
Gather the scraps, roll the dough and again cut as many circles as you can. Repeat this till the dough is almost exhausted.
Transfer the cookie dough circles to a greased baking sheet.
Whisk the remaining egg with 1 tsp of water and keep aside.
Brush the circle with egg-wash, place 1 tsp of the poppy seed filling gently in the centre of the circle as shown in the picture.
Fold the circle in from three sides to make a triangle as shown in the picture, gently crimp the corners to ensure they stay closed, leaving approximately about 1" surface of the filling exposed.
Brush the folded cookies with egg wash, bake for 15-18minutes.
Allow to cool, the cookies are now ready to serve.