Preheat oven to 160°C/320°F.
Combine cake flour, baking powder and baking soda, sift through and mix well.
Add hot water to instant coffee, mix well. Combine egg yolks, salt and sugar, mix well. Add in milk, thick coffee and corn oil, mix well. Sift in flour mixture, mix until combined.
Whisk egg whites over low/medium-low speed until large bubbles are formed. Add in cream of tartar, whisk until tiny bubbles. Add in sugar gradually, whisk until stiff peak (the peaks will point straight up and hold).
Add meringue into batter in 4 batches, mix gently using balloon whisk. Fold gently until well mixed with spatula. Tap mixing bowl on countertop for a few times to burst large bubbles.
Pour batter into 22-cm loose base tube pan (do not grease), tap tube pan gently again on countertop for a few times. Decorate the top with chocolate chips.
Put into preheated oven, bake at 160°C/320°F for 45 minutes, then at 180°C/355°F for another 10-15 minutes, until the top is golden brown.
Turn the pan upside down onto a wire rack (at least 6″ from countertop), set aside until fully cooled.
Unmould the coffee chiffon cake when it has fully cooled down.