in a mixing bowl, cream the butter with the back of a fork until it is smooth, about five minutes. Add the lemon zest and continue to blend until well mixed. Add the granulated sugar and mix until smooth, about two minutes longer. Add the egg and beat vigorously until lemony yellow batter forms, another five minutes.
Split the vanilla bean in half lengthwise. Using the tip of a sharp knife, scrape the tiny vanilla seeds into the batter and then stir to distribute evenly.
Slowly stir in 2 cups of the flour, and mix until the dough pulls away from the sides of the bowl, and a ball forms. Remove the dough from the bowl, flatten into a small disk, and wrap in plastic or foil wrap. Chill for 15 minutes.
Preheat the oven to 375°.
Generously flour a work surface and a rolling pin with part of the remaining 1/4 cup flour. Roll out the dough into a 1/4 inch thick sheet. Using a 2 inch round cookie cutter, cut out the cookies and transfer them to an ungreased baking sheet, about 3/4 inch apart. Gather up the scraps, apply more flour to work surface and rolling pin, and roll them out. Continue to cut out cookies until no dough remains.
Bake the cookies until Golden Brown edges appear around each cookie, 7 to 8 minutes. Remove from the oven and transfer to a wire rack. Let cool completely, about 30 minutes, then lightly dust with powdered sugar. Store in an airtight container at room temperature for up to one week. Makes about three dozen cookies.