For the heather sand, melt butter in a saucepan and brown slightly. Pour into a bowl and refrigerate for about 45 minutes.
Beat the re-solidified butter with a mixer until smooth. Gradually add the sugar, vanilla sugar, salt and milk. Then knead with the flour.
Make rolls of the dough and roll them in sugar. Wrap in plastic wrap and put in the refrigerator.
Cut cold rolls into slices, put the slices on a baking tray lined with baking paper.
Bake the heather sand at 180°C top/bottom heat for about 7 minutes.