Bring a saucepan of water to the boil over medium-high heat and boil eggs until soft-boiled (6½ minutes). Place eggs in an iced-water bath to stop cooking, then gently roll eggs on bench to crackle shells. Return eggs to iced water to cool completely, then peel.

Place chicken, onion powder, leek, parsley, cornflour and 2 tsp salt in a large bowl and mix with your hands until well combined, then lift chicken mixture out of the bowl and throw it back in, slapping against the side of the bowl, repeating until mixture is thoroughly combined and firm. Roll into 8 balls, then working with one at a time, place a piece of plastic wrap on a chopping board and flatten each ball out to 8cm x 12cm. Place one egg on top and carefully enclose with chicken and plastic wrap, keeping the shape of the egg. Transfer to a tray lined with baking paper, and repeat with remaining chicken and eggs. Chill until firm (20-30 minutes).

For tarragon mayonnaise, blend egg yolks, vinegar, mustard, tarragon and 1 tsp salt in a blender on high speed, scraping down sides, until finely chopped. Turn blender down to low-medium speed and, with the motor running, slowly drizzle in olive oil to emulsify – adjust thickness by adding water to thin or slowly drizzling in more oil to thicken. Cover and refrigerate until ready to serve.

Place flour, beaten egg and panko in separate bowls. Coat eggs in flour, shaking off excess, then eggwash, then roll in crumbs.

Preheat oil in a deep saucepan to 180°C. Deep-fry Scotch eggs in batches until golden (3 minutes; be careful, hot oil will spit). Remove with a slotted spoon, drain briefly on paper towels and serve hot with tarragon mayonnaise.