In a mixing bowl, add the crab meat, crème fraîche, spring onions and lemon juice and mix together, seasoning to taste.
Gently open the petals of the courgette flowers and spoon equal amounts of the crab mixture in between the petals, packing the mix in tightly and leaving enough space to be able to twist the petals back together. Ensure there are no gaps for the crab to escape out of.
Ideally, use a deep-fat fryer (if you haven’t got one, use a heavy-based saucepan) and heat the vegetable oil to 190°C/375°F. Test the temperature by putting a cube of bread in the oil – if it immediately starts to crisp up, you’re ready to go.
Meanwhile, make the tempura batter. Mix the plain flour, cornflour and baking powder together and slowly add the chilled sparkling water, whisking as you go. You’re aiming for the consistency of double cream (you may need to add more or less than the quantity given – be guided by the consistency).
Gently coat the stuffed flowers in the batter and, using a spoon for support, slowly lower a flower into the hot oil, flower-end first. After a few seconds, let it submerge fully and fry for about one-and-a-half minutes, until golden. Repeat for all four flowers.
Remove with a slotted spoon and place on paper towels to absorb any excess oil. Season with sea salt and they’re ready to serve.