Using an electric mixer, beat the butter, sugar, vanilla, fennel seed, and salt in a large bowl until light and fluffy. Beat in the egg. Add the flour and mix just until blended.
Transfer the dough to a sheet of plastic wrap. Shape the dough into an 8-inch-long log. Wrap the dough in plastic and refrigerate for 2 hours.
Preheat the oven to 350 degrees F. Line heavy large baking sheets with a silpat or parchment paper. Cut the dough log crosswise into 1/8 to 1/4-inch thick slices. Transfer the cookies to the prepared baking sheets, spacing evenly apart. Press the pine nuts decoratively atop the cookies. Bake until the cookies are golden around the edges, about 15 minutes.