Separate the eggs and leave it outside in room temperature for at least half an hour.
Preheat the oven to 325 F. Keep the 10 inch tube pan with detachable base ready. Do not grease the pan. It is important to leave the pan ungreased to enable the cake to rise.
In a large bowl, measure the sugar. Add the lemon zest and work it with the sugar until the sugar becomes grainy and very aromatic.
Now add the cake flour, salt and baking soda to the bowl and mix them well.
Make a well in the center of the dry ingredients and add all the wet ingredients in the well. Using a whisk, mix all the ingredients well together until there are no lumps and the batter becomes smooth.
To make the meringue - In a clean large mixing bowl, add the egg whites and start beating them until they are grainy and foamy.
Now add the cream of tartar and beat it on medium speed until soft peaks form. Soft peak is a stage where the beater whisk makes mark, but the peaks fall off the whisk. At this stage start adding the 2 tbsp of sugar gradually and beat the egg whites until they form stiff peaks. This is the stage when the peaks stand in an upright position without falling off the whisk.
Slowly add about ⅓rd of the egg white to the prepared batter and gently stir it until well incorporate. Use folding motion to mix the egg whites rather than quick mixing. Take care not to deflate the egg whites when mixing.
Add the remaining egg whites in 2 more batches and incorporate it well until no trace of egg white can be found in the batter.
Transfer the batter into ungreased tube pan. Run a knife or spatula through the batter few times to remove any air pockets from batter.
Bake for 50 – 55 mins until the cake bounces back when gently pressed in the center. Try to bake close to it actual baking time, since the cake would be gooey mess when undercooked. If the top seems to be browning a bit too quick, cover the pan with foil and continue baking to its actual baking time.
Once cooked, remove it from the oven and immediately invert it over a bottle or anything similar that could hold the pan safely upside down. Also make sure that there is space in between the counter and the pan so there is enough air flow to cool the cake.
Let the cake remain in this position until completely cool, about 2 hrs.
Now run a blunt knife or a spatula against the wall of the pan to loosen the cake.
Remove the cake with from the pan with its base intact. Now run a knife under the base of the pan and remove the cake carefully.
Place it on the serving tray with the bottom side on top and dust with confectionery sugar!
This cake remains fresh up to 3 days in room temperature, 10 days in the refrigerator and for up to a month in the freezer.