In a large bowl, sieve together the flour, potato starch, custard powder, and baking powder.

In a medium bowl, whisk the eggs and sugar together until blended. Add evaporated milk and water. Whisk until completely blended and foamy.

Pour about ½ cup of egg mixture into the flour mixture and whisk until the liquid has been absorbed. Add 1 more cup and whisk again until absorbed. While whisking, slowly add the rest of the egg mixture. Whisk until smooth. Add vegetable oil and whisk until blended. Let the mixture rest at room temperature for 1 hour.

Line a baking sheet with aluminum foil. Set it next to the stove.

Preheat both molds over medium heat until very warm. Turn the heat to medium-low. Spray the inside of the molds with cooking spray. Lay one mold on top of the prepared baking sheet. Pour batter into the mold until about 90% full. Place the other unfilled mold over the filled mold. Lift and keep in above the baking sheet. To spread the batter evenly on the bottom mold, tilt gently. By keeping both molds together, flip the whole thing upside down. Tilt the mold again. Return the molds to the stove over medium-low heat. Cook for 2 – 3 minutes or until golden brown, flip over and cook for another 2 – 3 minutes or until golden brown. Remove the waffle with tongs and transfer to a cooling rack. Cool for 2 minutes. Serve immediately.