Poppy Hamantaschen Cookies

Those cookies are traditionally in triangle shape, which represents the three corners of Haman’s hat, filled with poppy seeds or prune filling. The shape may also represent the three Patriarchs, Abraham, Isaac and Jacob, who inspired Queen Esther. More information can be found here.
Adapted from Smitten's Kitchen

Dough	Poppy Seed Filling
270 g All-purpose flour 100 g Powdered sugar 1 tbsp Finely grated lemon zest 1/3 tsp Salt 1 Large egg yolk 200 g Unsalted butter at room temperature 1 Egg, beaten for glazing	170 ml Milk 70 g Sugar 1 tbsp Finely grated lemon zest 80 g Poppy seeds, ground 40 g Dried cherries, roughly chopped 1 tbsp Lemon juice 1 tbsp Butter 1 tbsp Lemon extract

1. Place the flour, powdered sugar, lemon zest, and salt in the bowl of a food processor and pulse to blend. Add the butter and egg yolk and process until the mixture forms a ball. Scrape onto a sheet of plastic and wrap it tightly. Chill the dough for an hour or overnight.
2. If you can't find ground poppyseeds, use a spice mill or coffee grinder with whole poppyseeds. Heat milk, sugar, lemon zest, ground poppy seeds and chopped dried cherries in a small saucepan over medium heat. On a low simmer, cook until the seeds have absorbed the milk and the mixture has thickened, about 15 minutes. Add the lemon juice, and butter and cook for 2 minutes more. Turn the heat off and stir in lemon extract. Cool completely.
3. Preheat the oven 180C/350F. Line two baking sheets with parchment paper. On a lightly floured surface, roll out the dough to 4mm/1/4 inch thickness and use a cookie cutter or glass to cut 6cm/2.5 inch circles. Put a teaspoon of the filling in the center of each and press up the sides to form a triangle or any desired shape.
4. Place them on the prepared trays and brush the tops with the beaten egg for glaze. Return tray to the fridge for 20 to 30 minutes; chilling them again will help them hold their shape while they are baked. Bake until cookies are golden, about 15 minutes. If trays are on different racks, switch them after about 10 minutes.