Preheat the oven at 170 degree C.
Lightly whisk yolk and 20 g of sugar for 5 min at high speed till it doubles in volume, becomes thick and light yellow in colour.
Boil water and add coffee. Add in vegetable oil, SPRIG Japanese Yuzu Extract and the cooled coffee to the egg mixture. Stir in and combine well with a spatula.
Add in cake flour and cocoa powder to the liquid mixture, combine it well and set it aside.
In another bowl whisk egg whites for few seconds at low speed, till it becomes little foamy. At high speed, gradually add in sugar (spoon by spoon), beat till stiff or firm peaks form. ( It takes around 5 min for stiff peaks to form)
Fold in 1/3 portion of meringue to the cake mixture, fold in lightly. Do not over mix.
Gently fold in rest of the meringue with the cake mixture, combine it well.
Add the cake mixture into a Bundt pan. Bake the cake batter at 170 degree for an hour.