In a bowl, whisk together the egg yolk, mustard, saffron threads and whipped fromage blanc or Greek yogurt. Gradually whisk in the grapeseed oil, stirring continuously, and season with the cider vinegar and fine salt. The mayonnaise should be loose and collapse when placed on a plate rather than hold its shape.

Sift together the strong white bread flour, rice flour and cornmeal. Slowly add the sparkling water, stirring continuously, until the batter is runny but thick enough to coat.

Heat the oil in a deep fryer to 150°C (300°F). Remove the stems from the courgette (zucchini) flowers, leaving just 1 cm (½ inch). Remove the pistils and cut the flowers in half lengthwise. Coat one side of the flower in the batter then lower it into the deep fryer, battered side down. Cook for 4 minutes. Drain on paper towels and season with fleur de sel. Repeat with the remaining flowers.

Spoon a pool of saffron mayonnaise onto each plate, sprinkle with the sumac and arrange the courgette flowers on top, battered side up.