How to Make It
In a medium bowl, using a handheld electric mixer, beat the butter with the sugar, fennel and salt at medium speed until fluffy, 1 to 2 minutes. Add the egg yolk and vanilla and beat until combined. Add the flour and beat just until the dough comes together. Scrape the cookie dough onto a sheet of plastic wrap and form it into a log about 1 1/2 inches in diameter. Wrap and refrigerate the cookie dough until chilled, about 1 hour.
Preheat the oven to 350°. Cut the cookie dough into 1/4-inch-thick slices. Arrange the cookies about 1 1/2 inches apart on 2 ungreased baking sheets. Press 3 or 4 pine nuts into the center of each cookie. Bake the cookies for 13 to 14 minutes, or until they are golden brown around the edges. Let the cookies cool on the baking sheets for 5 minutes, then transfer them to a wire rack to cool completely.