Whisk cake flour, baking powder, sugar, and salt together in a bowl to incorporate air.

In a separate bowl, combine egg and milk.

Add the egg-milk mixture to the flour mixture, folding with a rubber spatula.

Add water gradually, observing the dough's consistency.

Once the dough is no longer floury, form it into a single mass by hand. Avoid overmixing.

Flour a work surface and spread the dough to about 1.5 cm thickness.

Flour the surface of the dough to prevent sticking.

Use a donut cutter to cut out donut shapes.

If a cutter isn't available, form donuts by hand.

Ensure the cutter is well-floured.

Fry the donuts in 165°C (329°F) oil.

Fry until the first side is light golden brown, then flip.

Fry the other side until it is also light golden brown.

Drain excess oil on a paper towel-lined rack.

Coat the hot donuts generously with castor sugar (superfine sugar).

Alternatively, place the sugar and donuts in a bag and shake to coat.

Serve immediately while piping hot.

If cooled, microwave for 10-20 seconds or warm in a toaster oven.

Optional: Use fresh cream instead of milk.

Optional Coating: Mix 2 teaspoons cinnamon powder with 100 g granulated sugar (or 4g cinnamon powder and 60g powdered sugar).