Preheat oven to 350F.

Lightly grease a 9×5-inch loaf pan.

In a medium bowl, whisk together flour, baking powder, baking soda and salt.

In a large bowl, cream together butter and sugar until the mixture is fluffy and resembles wet sand.

Beat in egg and egg white. Mix in 1/3 of the flour mixture.

In a small bowl, whisk together water, cocoa powder, vanilla and yogurt until mixture is smooth.

Add half of this mixture to the sugar mixture, followed by another 1/3 of the flour mixture.

Stir in remaining yogurt and remaining flour, stirring only until no streaks of flour remain.

Pour batter into prepared pan and spread evenly.



Bake for 55-60 minutes, or until a toothpick inserted into the center comes out clean.



Let cake cool in pan for about 10 minutes, then carefully cut along the sides of the pan to release the cake and turn it out onto a wire rack to cool completely before slicing.