| 1 | Preheat oven to 375 degrees. |
| 2 | Butter 2 baking sheets. |
| 3 | In a medium bowl, using a hand-held electric mixer set at high speed, beat the butter until creamy, about 1 minute. |
| 4 | Add the sugar and continue beating until the mixture is light in color and texture, about 2 additional minutes. |
| 5 | Beat in the yolk and vanilla. |
| 6 | Sift the flour, baking powder, cinnamon, and salt onto a sheet of waxed paper. |
| 7 | Using a wooden spoon, work the dry ingredients into the creamed mixture to form a stiff dough. |
| 8 | Scrape the dough onto another piece of waxed paper and form into a thick log about 8 inches long. |
| 9 | Wrap the log in the waxed paper and refrigerate until chilled and firm, about 1 hour. |
| 10 | Using a sharp knife, cut the chilled dough into 24 slices, each about 5/6 inch thick. |
| 11 | Arrange the slices about 2 inches apart on the prepared baking sheets. |
| 12 | Flatten the slices slightly with a fork, and top each with a walnut half. |
| 13 | Bake until golden brown, 10 to 12 minutes. |
| 14 | Let cool on the baking sheets for 2 minutes, then transfer to wire cake racks to cool completely. |
| 15 | The cookies will keep, stored in an airtight container at room temperature, for 3 days. |
| 16 | Makes 24 cookies. |
