Preheat the Oven:
Set the oven to 325°F (163°C).
Do not grease the chiffon cake pan.
Mix Dry Ingredients:
Sift cake flour, baking powder, and salt together.
Combine Wet Ingredients:
Whisk egg yolks, oil, coffee, vanilla, and half the sugar until smooth.
Combine Wet and Dry:
Gently mix the dry ingredients into the wet mixture until smooth.
Beat Egg Whites:
In a separate bowl, beat egg whites and cream of tartar until frothy.
Gradually add the remaining sugar and beat until stiff peaks form.
Fold in Egg Whites:
Carefully fold the egg whites into the batter, keeping it light and airy.
Bake the Cake:
Pour batter into the pan.
Bake for 45 minutes or until a skewer comes out clean.
Cool Upside Down:
Flip the cake upside down on a wire rack to cool completely.
Prepare the Whipped Topping:
Whip cream, powdered sugar, and espresso powder until fluffy.
Serve and Enjoy:
Slice, top with whipped cream, and devour.