This is from a cookbook called Best Recipes from the backs of boxes, bottles and cans. I think it might be the one you are looking for. Haven't we all made this?...or at least eaten a few!

Brownies

Two generations of American cooks have followed this recipe for brownies from the back of Baker's Unsweetened Chocolate package.

2 1-ounce squares Baker's Unsweetened Chocolate
1/3 cup soft butter or other shortening
2/3 cup all-purpose flour
1/2 teaspoon Calumet Baking Powder
1/4 teaspoon salt
2 eggs
1 cup sugar
1 teaspoon vanilla
1/2 cup chopped nuts

Melt chocolate with butter over low heat. Mix flour with baking powder and salt. Beat eggs well; then gradually beat in sugar. Blend in chocolate mixture and vanilla. Add flour mixture and mix well. Stir in nuts.
Spread in greased 8-inch square pan. Bake at 350 degrees F. for 25 minutes (for moist chewy brownies); or about 30 minutes, or until cake tester comes out clean (for cakelike brownies). Makes about 20 brownies.

Note: Recipe may be doubled; bake in greased 13x9 pan at 350 degrees F. for 25 or 30 minutes as directed. Makes about 40 brownies.