Cream butter and sugar with electric mixer on high for 3-4 minutes. Reduce speed to medium; mix in egg, vanilla and salt until combined. Reduce speed to low, add flour in 2 or 3 batches until just incorporated. Stir in fruit and nuts.
Flatten the dough into a disk, wrap with plastic and refrigerate for 2 hours.
Preheat oven to 350ºF. Roll dough into 1-inch balls and place on parchment-lined baking sheets. Bake 12-15 minutes until barely golden on the bottom. Transfer to racks and cool completely.
Roll evenly with confectioners sugar before serving.