Grandma Meade'S Orange Sunshine Angel Food Cake

Preheat oven to 275.rnSeparate egg yolks and egg whites into separate bowls and add cream of tartar and vanilla to the egg whites.
Sift flour 4 more times. I don't have a sifter, so I use a fine mesh sieve.
Beat yolks to incorporate as much air as possible, then beat egg white mixture until soft peaks form.
While you are beating the egg whites, heat the sugar, with no more than half a cup of water, in a small saucepan to about 230F. Use a candy thermometer to check temperature.
When sugar is ready, pour it into the egg whites in a thin stream while continuing to beat to incorporate sugar.
Fold in egg yolks, then fold in flour. Use a wire sieve to add flour gradually as you incorporate.
Pour batter into an ungreased angel food cake pan, and place in oven for 15 minutes. Then increase heat to 300 and bake another hour and 5 mintues. The cake will be just barely browning.
Remove the cake from the oven, and cool completely upside down in the pan. Don't worry, it will not fall out. Use a wine bottle or olive oil bottle to hold the cake with the tube. Run a knife around the outside edge of the pan to loosen cake from the edges, then push out pan and repeat on the top and center tube to release the cake.
Zest and juice orange.
Combine zest, butter and vanilla.
Whisk in parts of confectioners sugar and orange juice until the desired consistency is reached. Grandma's was always nearly spreadable.