Whisk all the ingredients, except the powdered sugar, together. Unlike with a regular tempura batter, there is hardly any gluten in this mix (or none if you make the substitution suggested), so you do not really have to worry about overworking the batter. There will be batter left over, but you need the excess to have enough to dip the heads in.

Heat the oil to 180c in a medium saucepan. This is best measured with a thermometer, although you can gauge temperature in a number of different ways if you are without. When the oil is hot enough, dip one flower head in the batter. The flowers will clump together, so use your fingers to separate them and hold them apart before dropping gently into the oil. You will probably be able to fry two at a time. When crisp and very lightly browned (a minute or two), use a slotted spoon to transfer the flower heads to kitchen towel to absorb the excess oil. Sprinkle with some of the powdered sugar. Repeat with the rest of the heads. Serve immediately.