Pre heat oven to 325 degrees
Separate the eggs. Place the yolks in the bowl of a stand mixer. Beat on high until they are a pale yellow and smooth but increased in volume. Slowly add in the sugar increasing speed until the yolks are thick and creamy. Whisk in the grapefruit juice. and blend well. Transfer to a large bowl.
Sift the flour over the whipped egg yolks and sugar and fold in by hand making certain there are no lumps. Fold in the vanilla and Cointreau. Set aside.
Sprinkle the salt over the egg whites. In a clean bowl of a stand mixer beat the egg whites until foamy and light. Add in the Cream of Tartar and beat on high until the whites hold stiff peaks- about 4 minutes total.
Delicately fold spoonfuls at a time of egg whites into the egg yolk mixture to loosen the batter. Gently fold in the remianing whites taking care not to deflate the batter.
Spoon the batter into a UNGREASED 10″ angel food cake pan with a removeable bottom. Do not fill the cake pan more than three quarters full.
If you have extra batter, you can make cup cakes.
Bake the cake on the middle rack at 325 degeees for 1 hour or until a cake tester comes out clean. Turn the cake upside down on the tube pan legs and let it rest at room temp overnight before frosting.
Remove the cake by using a sharp knife and then unmold the cake. You may need to run the knife under the base as well to loosen.
Pipe the frosting over the top of the cake leaving the sides bare. Chill until serving. The unfrosted cake freezed very well.
