Preheat oven to 350℉. Separate the egg whites from the egg yolks into two large mixing bowls. Set the egg yolks aside.
To the egg whites, add cream of tartar. Use an electric hand mixer to beat the egg whites until it becomes frothy like cappuccino foam.
Sprinkle in 150g of sugar, one spoonful at a time, mixing well in between each addition. After all the sugar has been added, keep beating until the meringue becomes stiff peaks. Set aside.
To the egg yolks, add the remaining 50g of sugar and mix to combine. Add 150g of the earl grey milk you steeped earlier, oil, and vanilla extract. Mix to combine.
With a fine mesh sieve, sift in the flour, baking powder, and earl grey tea leaves. Discard any large tea bits. Mix until just combined and smooth.
Add ⅓ of the egg white meringue to the egg yolk mixture. Fold together with a spatula until just combined. Add the rest of the meringue and fold together until the batter is airy and no streaks remain.
Pour the batter into a 10" ungreased tube pan, pouring in one spot and letting the batter flow into the rest of the pan to avoid creating air pockets. Lift and drop the pan on the table once or twice to help release any large air bubbles.
Bake for 35-40 minutes or until the edges just start to lightly brown and the top of the cake has a slight resistance when you press on it. Immediately flip the pan over and let the cake cool completely for at least 2-3 hours upside down resting on the legs of the pan or on a wire rack for airflow underneath.
When the cake has cooled, flip it back over and run an offset spatula or skewer around the outer edges of the cake. Flip it over on a serving plate or cake stand and pull the outer pan off and gently pull the inner tube upwards to release the cake.