Preheat oven to 350 degrees. In a mixing bowl, cream butter and sugar with an electric mixer on low speed until lightened in color. Add egg yolks and beat until smooth. With the mixer on low speed, add flour and salt and mix until smooth. The dough will be stiff.Form dough into 1-inch rounds. Place on lightly greased baking pans and press a pecan or cherry half into each round. Bake until cookies are golden, about 9 to 11 minutes. Remove to a rack to cool.