Preheat oven to 350 degrees.
Combine first 3 ingredients in a heavy saucepan. Cook over medium low heat stirring constantly until chocolate and butter melt.
Remove from heat. Stir in vanilla, flour, and chopped pecans.
Drop by teaspoonfuls onto ungreased cookie sheets. Press a pacan half into the center of each cookie.
Bake for 7 minutes.
DO NOT OVERBAKE.
Remove cookies to wire racks to cool. Store in an airtight container.