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1
Combine the mung bean flour and wheat flour in a bowl. Add water gradually, whisking to a thin, smooth, pourable batter with no lumps. The batter should be translucent when spread: if it holds opacity at 2 mm thickness, thin it further with water. Rest for 10 minutes.
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2
Fry the guo ba zi in hot oil until pale gold and rigid throughout. Transfer to a rack. They must remain bone-dry and brittle; any residual softness disqualifies them from the dish.
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3
Heat a large circular flat griddle or crêpe pan over high heat. The griddle is ready when a drop of batter sets and firms at its edges within 5 seconds of contact.
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4
Ladle one quarter of the batter onto the griddle and spread immediately in a single circular motion to the thinnest possible layer. This is where the dish lives or dies: a crepe spread too thick will never become translucent and the structure will be doughy rather than delicate; the batter must reach near-translucency within 20–30 seconds on the hot surface.
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5
Crack one egg directly onto the wet surface of the crepe. Spread the egg over the batter with the back of a spatula so it forms an even, thin film rather than a pooled layer. The crepe is ready to receive toppings when the egg loses its raw sheen across the full surface.
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6
Working while the crepe is still on the heat, brush hoisin sauce and Sichuan chili paste across the egg surface. Scatter scallion, coriander, and ground Sichuan peppercorn. The sauce should sizzle gently on contact with the hot crepe.
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7
Lay one guo ba zi crisp across the centre of the crepe. Fold the crepe over in thirds to enclose the crisp. The finished parcel should yield a sharp crack when pressed lightly at the centre, confirming the crisp has retained its structure. Serve within 3 minutes.