Preheat oven to 325℉ (160℃).
Line a 6x3 inch aluminum foil loaf pan with wax paper.
With elec. mixer, beat butter in a small bowl until soft and light.
Gradually add sugar, beating until light and fluffy.
Beat egg in another small bowl.
Gradually add to the butter-sugar mixture, beating until light and fluffy.
Stir in vanilla. Stir in flour to moisten; beat until light and smooth.
Spoon batter into prepared pan and distribute evenly.
Bake about 55 minutes until edges separate from pan.
Top should be golden and spring back when lightly touched in center.
Cool in pan 15 minutes. Loosen sides and remove by lifting ends of wax paper.
Cool on a wire rack.
Sprinkle with powdered sugar, if desired.