Place yogurt, sugar, vanilla and lemon or orange rind in the mixer and mix until just combined. Add egg yolks one at a time, beating well after each addition.
Sift together flour, cornstarch and baking powder and add to the egg yolk mixture. Beat to combine. Remove bowl from the mixer.
Beat egg whites until foamy, add 1 tablespoon sugar and continue beating until thick and firm. Fold in egg whites into batter.
Butter a 12 in tube cake pan (24 cm) and sprinkle sugar on bottom and sides.
Pour batter into cake pan and bake cake in a preheated moderate oven to 350ºF (180ºC) for 40 minutes or until tester comes out clean.
Remove cake from the oven and cool for 10 minutes.
Invert cake unto platter and cool completely.
Dust confectioner’s sugar before serving.