Cook butter and chocolate in a small saucepan over low heat, stirring often until melted.

Beat eggs at medium speed with an electric mixer 5 minutes. Gradually add sugar, beating until blended. Gradually add chocolate mixture, flour, and vanilla, beating until blended. Stir in 1/2 cup pecans.

Pour mixture into a lightly greased 9-inch pieplate.

Bake at 350° for 35 to 40 minutes or until center is firm. Cool. Top each serving with vanilla ice cream and chocolate syrup; sprinkle with remaining chopped pecans.