Preheat oven to 340F (170C). You will also need a chiffon cake pan or 7 to 10" aluminum spring-form pan (I do not recommend a non-stick or other material pan). Do not grease the pan - the batter needs to stick to the sides of the pan as it bakes.
Put 1 tbsp of the tea leaves in a heat proof bowl or measuring cup, and add 6 tbsp hot water. Set aside to steep. Once cooled, remove the tea leaves and measure out 4 tbsp of the steeped tea. Set aside.
Take 2 tsp of the tea leaves and blend in a food processor or use a mortar and pestle to grind to a fine powder.
Separate the 3 egg whites and yolks - make sure your egg whites stay cold - this will help your cake get a good rise in the oven.
In a large bowl, add the egg yolks and add 1/3 of your 80g of sugar. Whisk together. Set aside.
Add the 4 tbsp steeped tea, 3 tbsp oil and the powdered tea leaves. Whisk to combine.
In three batches, sift in the 75g of cake flour and 1 tsp baking powder, whisking well after each addition. Make sure there are no lumps. Set aside.
Using a stand mixer and a clean bowl (make sure it is clean, or your egg whites won't whip properly!), whisk the cold egg whites on medium speed till they start to get foamy and bubbly (about 30 seconds). Add 1/3 of the sugar and continue whisking.
Keep whisking and adding sugar a little at a time. Turn the speed to high and whisk till stiff peaks form (about 5 minutes total). You can test for stiff peaks by dipping the whisk in the egg whites and if it stays standing and just the tip takes a tiny bow. It should hold its peak shape.
Using a spatula, gently fold in the egg whites into the prepared cake batter in 2 -3 increments. Making sure there are no white streaks of egg white after each addition, but also don't over mix it or you will loose all that air.
Once the egg whites are mixed into the batter, carefully pour the batter into a cake pan. Try not to swirl the batter round to pan. Just pour into one spot and let the batter slowly fill up the pan. This will also prevent air pockets from forming.
Give the pan a few gentle taps on the counter to release any remaining air bubbles. And run a toothpick through the batter, again to release any trapped air bubbles. This will ensure an even rise.
Bake in the preheated oven for 30-35 minutes. Careful not to over cook the cake (if it looks like it is starting to brown on top, loosely cover with some aluminum foil to finish baking it). When it is done, it will be set on top, and a clean toothpick inserted into the centre should come out clean.
As soon as you take this out of the oven, you will need to turn the pan upside down and let the cake cool upside down. Place it on a baking rack, or perch it on two mugs to hold it up and not squish the top of the cake. It will shrink a bit, but it should not have any big indents in the top of the cake.
Allow to cool completely, then use a spatula to carefully loosen the edges from the sides of the cake and remove the sides of the pan.