Combine baking soda, baking powder, salt, and sugar in a bowl.

Add water to the dry ingredients and stir well to dissolve.

Gradually add the wet mixture to the all-purpose flour, stirring gently for a few seconds to start combining.

Add vegetable oil to the dough and mix until well combined and a smooth dough forms.

Cover the dough and let it rest for 4 hours at room temperature to allow it to rise.

Heat vegetable oil in a wok or deep frying pan to 350°F (175°C).

Dust a work surface lightly with flour to prevent sticking.

Roll the dough into a long sausage shape.

Cut the dough into 1-inch pieces, form each piece into a small ball, and then roll it out into a thin circle (about 4-5mm thick). For the X-shaped style, cut the dough into 2-inch pieces.

If making the X-shape, dab a little water in the center of each piece and stick another piece to it to form an X shape.

Carefully drop the donuts, 2 at a time, into the hot oil and fry until they rise to the surface and are golden brown on all sides.

Remove the fried donuts and drain on paper towels to remove excess oil. Serve warm.