Sharon Tyler Herbst calls these tender fruit-filled cookies one of the prettiest in her chapter on holiday treats. They are small, almost bite-sized, and filled with lekvár, which here in the United States is typically prune butter but in Central and Eastern Europe can be any fruit preserve. They could also be filled with rhubarb.
The dough is lightly-sweet and pastry-like, made with cold butter cut into a mixture of flour, powdered sugar, baking powder, salt and cardamom. An egg yolk beaten with vanilla extract holds the crumbly mix together for rolling out. Once the shapes were cut, filled and folded, I brushed each with egg white and sprinkled them with coarse sugar before baking.
These delicate, delicious cookies are Icelandic in origin. Hálfmánar means crescents or half-moons.