1. Whisk egg yolk with salt. Add in oil and milk and mix well.
2. Sift flour and baking powder into the egg yolk mixture.
3. Beat egg whites with cream of tartar until foamy and then add in sugar and beat till soft peak.
4. Fold in half of the egg whites into the mixture and mix well. Then add in the other half and mix them evenly.
5. Fill the mixture into the cups
6. Bake at pre-heated oven at 160c for 20mins. Leave cool.
7. Make a small hole at the middle, pump the custard cream into the chiffon.
8. You can either chill before serving or have it straight after filling in the cream.