Start by making the batter. In a large bowl, mix together the rice flour, salt, turmeric and egg. Add the coconut milk and water and whisk until the batter is smooth and runny. Set aside to stand for at least 10 minutes.
Next, make the slaw. In a different large bowl, combine the shredded cabbage, carrots, spring onions and herbs. Set aside while you make the nuoc cham chay.
To make the nuoc cham chay, add the lime juice, sugar, soy sauce, chillies and garlic into a small bowl and mix well. Pour around half of the sauce over the slaw and mix. Taste, adding one tablespoon at a time until you’re happy with the ratio of sauce to slaw. Pour the remainder of the sauce into a small serving bowl for dipping.
To make the banh xeo, heat a teaspoon of oil in a non-stick frying pan (see notes) over a medium flame, swirling it around to coat the pan. When the frying pan is piping hot, pour around ¾ of a ladleful (see notes) of batter into the pan. Working quickly, swirl the pan around so that the batter reaches the edges of the pan.
Let it cook for 2 to 3 minutes, until small bubbles form and the batter firms up. While it’s still cooking in the pan, add a handful of the slaw to one side of the pancake and let it heat up slightly until the bottom of the pancake is slightly crispy and golden. Fold the banh xeo over the filling and gently slide onto a plate. Repeat with the rest of the batter until you have 6-10 pancakes (see notes).
Serve the banh xeo with fresh green leaves, lots of herbs and the rest of the nuoc cham chay. To eat it, start with a lettuce leaf base, layer on other leaves and herbs and top with a piece of banh xeo. Roll it up as best you can (this will depend on the type of lettuce you’re using), dunk it into the dressing and enjoy!