Preheat oven to 375 degrees. Line 2 baking sheets with parchment paper. Put raisins in small bowl, add orange juice and let soak for 10 minutes or until plump.
Put butter and sugar into large bowl, mix well with wooden spoon, then beat in egg yolk and vanilla. Sift flour and salt into butter mixture and add oats and chopped hazelnuts. Drain raisins, discard any orange juice not absorbed. Add raisins to butter mixture, stir until all ingredients are combined.
Drop tablespoonfuls of dough onto baking sheets, spaced well apart. Flatten slightly and place 1 whole hazelnut in center of each cookie.
Bake 12-15 minutes or until golden brown. Let cool on baking sheets 5-10 minutes, then carefully transfer to racks to cool completely.