Grease and flour a 12-cup bundt cake pan. Heat oven to 350°.
In a medium bowl, beat the egg whites until foamy. Beat in cream of tartar and 1/2 cup of the sugar; continue beating until stiff peaks form.
In a large mixing bowl, cream butter and the remaining 1 1/2 cups of sugar until light and fluffy. Beat in the egg yolks, one at a time, beating well after each addition. Blend in the orange zest and orange juice. Sift the flour with the baking soda and salt. Add a third of the flour mixture to the batter, blending on low speed. Blend in half of the yogurt. Repeat with another third of the flour mixture and the remaining yogurt. Blend in the remaining flour until smooth. Fold the beaten egg whites into the batter until thoroughly incorporated.
Spoon the batter into the prepared pan and bake for 50 to 55 minutes, or until a toothpick inserted in the center of the cake comes out clean. Cool in pan for 10 minutes; turn out onto a serving plate or rack to cool completely. Dust with powdered sugar or drizzle with a glaze.