It has taken me years to get this one right. Yield:  3-4 dozen cookies (depending on size) 1/3 cup butter, softened 1/3 cup vegetable shortening 1/2 cup granulated sugar 1/2 cup brown sugar 1 egg, beaten 1 teaspoon vanilla 1 1/2 cups flour 1/2 teaspoon salt 1/2 teaspoon baking soda 1/2 to 1 cup chocolate…