Special equipment – 10-inch (25cm) tube pan with removable bottom.
Preheat the oven to 325°F (160°C) with the rack in the middle position.
Using a mortar and pestle or an electric coffee grinder, grind 1 tablespoon of the loose leaf tea until fine. Set aside. If you’re using tea bags, skip this step.
Bring the water to a boil in a small saucepan. Add the remaining 2 tablespoons of loose leaf tea or, if using, the 4 tea bags. Cover and let steep according to packaged instructions, about 5 minutes. Strain if using loose leaf tea. Let cool to room temperature. If necessary, add additional water to measure 2/3 cup (160 ml).
Whisk together the egg yolks, ½ cup (100 g) of the sugar, oil, salt, ground tea leaves and steeped tea in a large bowl. Add the flour and gently whisk just until smooth. Set aside.
Beat the egg whites in another large bowl with an electric mixer on medium speed. When the whites become frothy, add the salt. When the whites begin to increase in volume and lose their opaqueness, gradually add the remaining ¼ cup (50 g) sugar. Beat until whites are stiff and glossy, but not dry.
Fold ¼ of the whites into the egg yolk-tea mixture to loosen the batter, then gently fold in the remaining whites just until fully incorporated, being careful not to deflate.
Pour batter into an ungreased 10-inch (25-cm) tube pan with removable bottom. Gently run a knife or spatula through the batter to break up any large air pockets – be sure to reach the bottom.
Bake for 30-35 minutes, or until a toothpick inserted in the middle comes out clean. Let cool upside down – suspended over the neck of a wine bottle works best.
Once the cake is completely cooked, remove it from the pan by running a knife around the sides and carefully pushing the bottom out. To release the tube portion from the cake, carefully run a knife between the cake and bottom of the pan.
To make the optional frosting, beat together the cream and sugar in a bowl with an electric mixer on medium-high speed until soft peaks form.
The outside of the cake can be quite crumbly. To keep the frosting crumb-free, spread a thin layer of the whipped cream over the cooled cake. Refrigerate the cake (and remaining whipped cream) until set – 5 to 10 minutes. Then frost the cake with the remaining whipped cream. The cake should be frosted just before serving.