Make the batter: Combine the Bánh Xèo mix (or rice flour and cornstarch), coconut milk, club soda, turmeric, and salt. Whisk until smooth. Rest for at least 30 minutes at room temperature — this step is non-negotiable for a crispy, non-gritty crepe.
Prep the filling: Season pork belly and shrimp lightly with salt and pepper. Have all your herbs, greens, and dipping sauce ready before you start cooking.
Heat the pan: Place a 16-inch non-stick pan over high heat. Add 1 tsp of neutral oil and let it get screaming hot.
Char the filling: Add sliced onion, then pork belly, then shrimp. Let them sizzle undisturbed until charred on the edges. This smoky char is the flavor foundation of a great Bánh Xèo.
The swirl: Pour in one ladle of batter and immediately swirl it up the sides of the pan in a circular motion to create lacy edges.
Steam: Scatter mung beans and bean sprouts over one half of the crepe. Cover with a lid for 30–45 seconds.
Crisp: Remove the lid and let the Bánh Xèo cook uncovered for another 60–90 seconds until all steam has evaporated and the edges are golden and pulling away from the pan.
Fold and serve: Fold the crepe in half over the filling and slide onto a plate. Serve immediately with herbs, greens, and Nước Chấm for dipping. Repeat with remaining batter, adding fresh oil to the pan each time.