Brew the tea
Steep the Earl Grey tea in hot water for 10 minutes. Cover while steeping. Let it cool fully.
Prepare the pan
Use an ungreased chiffon or tube pan. Do not line or grease it. Preheat oven to 325°F (165°C).
Mix dry ingredients
In a large bowl, whisk cake flour, 1 cup sugar, baking powder, and salt.
Mix wet ingredients
In another bowl, whisk egg yolks, oil, cooled tea, and vanilla.
Combine batter
Add wet mixture to dry ingredients. Whisk until smooth and pourable.
Whip egg whites
Beat egg whites with cream of tartar until foamy. Slowly add remaining ½ cup sugar. Beat until soft peaks form.
Fold carefully
Stir one-third of egg whites into batter. Gently fold in the rest using a spatula.
Bake
Pour batter into pan. Smooth the top. Bake 50–60 minutes until the top springs back.
Cool upside down
Invert the pan right away. Let cool fully before removing.