To make the fennel salt, toast the fennel seeds in a dry pan over high heat for 2 minutes or until golden & crackling, remove & cool slightly. Once cooled, place the fennel into a spice grinder or mortar & pestle & grind to a smooth powder. Add it to a bowl & add in the sea salt flakes, mix well & set aside.
To make the aioli, add the egg yolk, dijon mustard & minced garlic to a bowl, whisk to combine. Once smooth, slowly pour in the extra virgin olive whilst continuously whisking to create an emulsion (pour it very slowly otherwise it will split). Once the extra virgin olive has been added, add in a few splashes of the lemon juice, whisking and adjusting to your preference. Season to taste & place in the fridge until you're ready to serve.
Pour enough canola oil into a large high rimmed pan or pot to fill it by half. Place over a high heat & heat to 180°c-350°f. (Use a thermometer for best results)
In a mixing bowl, add in the plain flour & baking powder, mix to combine. Place the prepared prawns into the flour mix in batches and completely coat, dusting off any excess flour. Place onto a plate.
Fry the prawns in the hot oil for 2 to 3 minutes or until golden & crispy. Remove and drain on a wire rack over a baking tray or on some kitchen cloth. Season to taste with the fennel salt. Serve with aioli & a lemon wedge.