Combine flour, cornmeal, salt and soda in bowl.
Beat butter and sugar in medium-size bowl until creamy and smooth. Beat in egg yolks, rind and extract until fluffy. Stir in flour mixture and walnuts. Divide dough in half; flatten. Wrap in plastic. Refrigerate 30 minutes.
Heat oven to 350 degrees F. Coat baking sheet with nonstick cooking spray.
On lightly floured surface with floured rolling pin, roll half of dough 1/4 inch thick. With floured 3-1/2-inch round or star-shaped cookie cutter, cut out dough. If using rounds, cut each round in half. Place 1 inch apart on prepared sheet. Repeat with remaining dough.
Bake in 350 degree F oven 10 to 12 minutes or until lightly golden. Cool on wire rack.
Melt chocolate in small saucepan over low heat, stirring constantly. Remove saucepan from heat. Dip cookies into chocolate. Place cookies on baking sheet lined with waxed paper. Let stand until chocolate hardens, 1 hour. Freeze or store at room temperature. Makes 30 sandies.