Mix the wet ingredients – In a large bowl, whisk eggs and sugar until pale and slightly thick. Add evaporated milk, water, vanilla, and oil. Stir until smooth.
Combine the dry ingredients – In another bowl, whisk together flour, baking powder, custard powder, and tapioca starch.
Make the batter – Slowly fold the dry ingredients into the wet mixture. Stir gently until just combined. Batter should be smooth but not too thick.
Rest the batter – Let it sit for at least 30 minutes (or up to 1 hour) to hydrate and improve texture.
Preheat the pan – Heat a bubble waffle pan (stovetop) or bubble waffle maker (electric). Lightly grease with oil.
Cook the waffle – Pour about ¾ cup of batter into the pan. Close and flip quickly to spread evenly. Cook 2–3 minutes, flip, then cook another 2–3 minutes until golden brown.
Serve – Carefully lift out the waffle. Cool for 1 minute so the bubbles crisp up. Serve plain, or roll into a cone and fill with ice cream, fruit, or toppings.
