Mix the flour, yeast, icing sugar, warm milk (make sure it isn't too hot or it'll kill the yeast), egg to a bowl or stand mixer and mix until well incorporated.
Add the salt and the butter, lump by lump until mixed.
Cover and set aside for an hour or overnight in a cool place.
To make the filling:
Grind up the poppy seeds in a Vitamin or similar.
In a small saucepan on a low heat, add the milk, butter, sugar, honey, lemon zest. Heat gently until the butter is melted, then add the poppy seeds. Stir in well then remove from the heat and leave to cool.
To assemble:
Put the pastry onto a floured clean surface and divide into 15 balls (around 45g each).
Roll out each ball into a strip approximately 11 cm (4 inches) wide by 18cm (7 inches) long. The ends should be slightly thinner.
Pick up a ball of the ground poppy seed mixture with your hands or a spoon (it's quite solid so can be handled) and roll with your hands into a thin sausage about 15cm long (6 inches). Place in the middle of the pastry strip.
Fold over the pastry, sealing it with your fingers. Then push up the ends to make a crescent shape. Place on a silpat, silicone sheet or parchment paper on a flat baking tray.
Preheat the oven to 180C (360F) and continue to make the crescent shapes with the pastry and poppy seed mixture. You will probably need 2 baking trays if you are baking them all at once.
When the crescents, kifli, are all made, brush them with egg.