Preheat the oven to 350 F (175 C).

To prepare the orange fluff cake, pour the flour, half of the sugar, baking powder, and salt into a bowl. Mix well with a whisk until well combined

With a spoon, create a well in the center and slowly add the orange juice, egg yolks, orange zest, vanilla extract, and melted butter. Whisk until smooth.

Using a stand-up or hand-held mixer, whisk the egg whites with the cream of tartar until frothy. Slowly add the other half of the sugar while whisking, until stiff peaks form.

Fold the egg whites into the egg yolk/flour mixture with a spatula a little at a time, with slow movements from bottom to top.

Pour the mixture into a 10-inch tube pan and place it in the oven. Bake for around 40 - 50 minutes. (It is very important that the mold is not greased and floured when we pour in the batter).

Once the cake is out of the oven, let it cool upside down in its mold for 2-3 hours or until it cools down completely. When cold, release the cake from the mold with the help of the dull side of a knife blade.

Before serving, prepare the glaze: In a small bowl, mix together the confectioner’s sugar with the orange juice and zest. Pour the glaze evenly on top of the cake and serve.