Do not preheat the oven. Grease 10 inch tube pan or loaf pan, and line bottom with wax paper or parchment paper.

Sift together the flour, baking powder and salt. Set aside.

In a large bowl, beat the butter, shortening, and sugar on low speed for 10 minutes. If you dont have a mixer try to whip it by hand until its as fluffy as u can get it. Add the eggs one at a time, blending well after each addition. Alternately add the flour mixture ,milk, and yogurt mixing well. Add the vanilla.

Pour batter into the prepared pan. Set the oven temperature to 350°F. Bake for 1 hour or until a toothpick inserted into the middle of cake comes out clean. Allow cake to cool in the pan for 30 minutes. Remove to a cake rack and cool for at least 2 hours.