Marble Pound Cake

1.5 cups white sugar
3/4th cup butter, softened
2 heaped cups cake flour
3/4th cup milk
1 heaped teaspoons baking powder
1.5 teaspoons vanilla extract
a pinch teaspoon salt
3 eggs
3 tablespoons unsweetened cocoa powder

In a large bowl, with electric mixer at low speed, beat sugar and butter or margarine until blended. Increase speed to high, and beat until light and fluffy. vanilla, salt, and eggs; beat at medium speed until well mixed.
Mix flour and baking powder separate.
Add flour and milk alternatively in parts.Beat at medium speed for a minute.Increase speed to high, and beat batter 4 minutes longer.
Remove about 2 cups batter to a medium bowl. With a wire whisk or fork, beat cocoa into batter in medium bowl until well blended.
Grease a 10 inch tube pan or a loaf pan. Alternately spoon vanilla and chocolate layers into prepared pan. With a large spoon, cut and twist through batters to obtain marbled effect.
Bake at 350 degrees F (175 degrees C) for 1 hour, or until a toothpick inserted in the center of the cake comes out clean.
Cool cake in pan, and on a wire rack, for 10 minutes.
Remove cake from pan, and cool completely.