1 cup (2 sticks) margarine
4 ounces unsweetened chocolate, coarsely chopped
1-3/4 cups sugar
1 tablespoon vanilla
¾ cup flour
1 cup chopped toasted walnuts (optional)
Preheat oven to 325 degrees. Lightly grease a 9 x 12-inch pan. Place margarine and chocolate in a small saucepan over a very low heat. Cook, stirring, until chocolate has melted. Turn off heat and stir until smooth. Cool to room temperature.
Stir in sugar. Beat eggs and stir in quickly one at a time. Add vanilla and then flour until just combined. Stir in nuts, if using. Pour into prepared pan and bake for 25 to 30 minutes. Cool in pan and cut into bars. Freezes well.