Melt butter in a microwave for 5 seconds on each side, or use room temperature butter. Use a stand or hand mixer to blend in butter and sugar. Beat on high for 2 minutes, until fluffy. Add in 1 egg, orange juice and vanilla. Add baking powder and salt, then slowly add in sifted flour. Mix until evenly blended, but be careful not to over mix.
Cover dough, once formed into a ball, with plastic wrap. Chill dough overnight.
After dough has chilled, preheat oven to 350 degrees.
Use a floured surface to roll out the chilled dough until dough is ½ inch thick. Begin cutting circles in the dough (this recipe used a 3-inch cookie cutter). Re-roll excess dough to make sure you have enough for the amount of cookies you wish to bake.
Add a spoonful of poppy seed filling to each cookie and spread out evenly. Begin folding the bottom of each circle to resemble the bottom shape of the heart. Fold over the top to also mold into the top of the heart shape. You can use a cookie cutter as a shaping tool to help form each cookie. Brush each cookie with egg wash before baking.
Bake cookies for 15 minutes, or until they are golden brown.