Preheat to 325F.
Grease and lightly flour a 4.5x8.5" loaf pan.
In the bowl of an electric mixer at medium speed,
beat butter and 1/2 c. sugar until
light and fluffy, about 2 min.
Add the yolks; beat well.
Blend in orange extract and orange rind.

In another bowl, stir together flour, baking powder,
baking soda and walnuts. Beating until smooth,
after each addition alternately add sour cream
and dry ingredients to batter.

With clean beater, beat egg whites until they are foamy.
Beating well after each addition and adding
only 1 tbs. at a time, add remaining sugar.
Continue beating until egg whites are thick and glossy.
Gently fold whites into batter.

Transfer to prepared pan.
Bake until a toothpick inserted in center
comes out clean, 40-50 min. Do NOT overbake.
Cool in the pan for 10 min.;
then invert onto a wire rack and cool completely.
Makes 16 servings.