Beat butter in a large mixing bowl with an electric mixer on medium to high speed for 30 seconds. Add granulated sugar, and beat until combined, scraping sides of bowl occasionally. Beat in bourbon until combined. Beat in as much of the flour as you can with the mixer. Stir in any remaining flour and the pecans with a wooden spoon.
Form dough into 1-1/4-inch balls. Shape each ball into a 2x1-1/2-inch log; shape logs into crescents, tapering ends slightly. Place crescents about 1 inch apart on an ungreased cookie sheet.
Bake in a 325 degree F oven for 20 minutes or until bottoms are lightly browned. Transfer cookies to wire racks and cool. Sprinkle cooled cookies with chocolate or regular powdered sugar. Makes 36 crescents.