In a stand mixer, combine all-purpose flour, baking powder, baking soda, sugar, and salt. Add the egg and water, then knead on low speed for 7-9 minutes until the dough is soft and elastic. If kneading by hand, mix the dry ingredients, incorporate the egg and oil, then knead for about 10 minutes. Let the dough rest for 1 hour, covered, in a warm spot until it slightly puffs up.

After resting, roll the dough onto a floured surface into a rectangle about 1 cm thick. Brush the top with a light coat of vegetable oil to prevent drying. Cover the rolled dough with a clean cloth or plastic wrap and let it rest for an additional 2 hours.

Once rested, use a sharp knife or pizza cutter to slice the dough into 3 cm wide strips. Lightly wet the edges of each strip with water to help them stick together. Stack two strips on top of each other, pressing down gently in the center.

In a deep pot, heat vegetable oil to 180-190°C (400°F). Carefully stretch each strip of dough slightly before placing them in the hot oil. Fry for about 1 minute, turning until golden-brown and puffed.

Quickly transfer the youtiao to a wire rack lined with paper towels to drain excess oil. Let them cool for a few moments before serving.