Step 1Heat the oven to 375 degrees. Sift together the flour and baking powder in a medium bowl. Stir in the fleur de sel.
Step 2Cream the butter in the bowl of a stand mixer fitted with the paddle attachment (or in a medium bowl using a hand mixer). With the tip of a knife, scrape the vanilla bean seeds into the butter. Continue to beat until blended. Add the sugar and mix until light and fluffy, making sure to scrape down the sides of the bowl. Beat in the rosemary or thyme, then beat in the egg just until blended.
Step 3Beat in the flour mixture just until the dough is well-mixed. Remove the dough from the bowl and flatten into a disk. Wrap the dough in plastic wrap, and chill it for 15 minutes.
Step 4Remove the plastic wrap and roll the dough out on a lightly floured surface to one-fourth-inch thick. Cut out cookies into 2-inch squares, rounds or triangles. Place them on a buttered cookie sheet. Lightly brush the tops of each cookie with milk, then sprinkle with a little rosemary or thyme. Place the cookie sheet in the refrigerator to allow the cookies to chill an additional 15 minutes.
Step 5Bake the cookies for 9 to 12 minutes, until the cookies have faint coloring around the edges. Remove the tray from the oven, and transfer the cookies to a wire rack to cool.