Warm milk to just above room temperature. Dissolve the yeast in the milk, set aside.
In a medium bowl, stir together the flour, baking powder and salt. Rub in the butter using fingertips until the mixture is mealy. Stir in the egg yolks and milk mixture. Knead the dough together and then refrigerate overnight.
Preheat oven to 180 degrees C.
Dust a clean, dry surface with icing sugar. Knead the dough for a few minutes. Carefully roll out your dough to 1/2cm thickness. Cut out circles with a cookie cutter. Place a teaspoon of jam on the centre of each circle, fold the dough over and seal the edge with a fork.
Place on flat baking trays. Bake in preheated oven for 12 to 15 minutes. Dust with icing sugar. Do not store in an airtight container or they will become soggy.