Peel lotus root and slice thinly. Put into water with a dash of vinegar (to prevent discoloration).
Skin sweet potatoes and slice thinly. Soak in water for 15-20 minutes.
Break the egg into a bowl and pour in the beer or soda water. Whisk vigorously until frothy then add the sifted flours and baking powder to mix until just combined. Do not over-mix; the mixture should be lumpy.
Heat oil in a wok, dip sweet potatoes, lotus root, prawns and enoki mushrooms in plain flour, then shake off excess flour.
Dip into tempura batter and drop them into the oil in batches.
When they are light golden, remove with a pair of chopsticks. Drain on absorbent paper.
Fry small amounts at a time; make sure enough time is allowed for the oil to return to the correct temperature before frying the next batch of ingredients.
Serve tempura with dipping sauce.
Combine all the ingredients together in a small mixing bowl. Allow the flavours to blend for at least an hour before using the sauce.