Preheat oven to 300 degrees F (175 degrees C). Grease an 8-inch square baking pan.
Melt the butter or margarine over low heat. Pour into large mixing bowl and stir in carob powder, sugar, salt, flour, and vanilla. Mix in egg whites and walnuts. Spread the dough evenly into the baking pan.
Bake for 30 minutes. Let cool in pan for 10-15 minutes before cutting.