Melt chocolate and margarine over low heat in a medium saucepan. Add butter extract and chopped pecans; stir well. Remove from heat, and set mixture aside.
Combine flour, sugar, eggs, and vanilla in a large mixing bowl; add chocolate mixture, and stir until moistened.
Spoon 3 tablespoons batter each into paper-lined muffin pans. Bake at 325° for 30 to 35 minutes or until cupcakes test done. Cool in pan 10 minutes; remove to wire rack to cool completely. Sprinkle with powdered sugar, if desired.