Put ground almonds, powdered sugar and some (not all) of the egg whites in a large mixing bowl and mix well. Add additional egg whites until you get the consistency you are looking for.
Melt butter and brush the molds well. Put some flour in a wide tray or bowl and dip the whole forms in the flour. Shake off any loose flour. Make sure the entire inside of the mold is covered in butter and flour.
Kransekake can be stored in a box with a tight lid. A few of days before the cake is to be served put a couple of pieces of soft bread into the box to make it chewy. Make sure that the bread do not touch the cake itself.