Line a square baking tray –approximately 23x23cm in size – with cling film and put it in the fridge to cool
To make the custard, pour the milk in a heavy-bottomed saucepan and set it over a low heat. Add the strip of lemon zest and bring to a simmer
Meanwhile, in a large glass bowl, whisk the egg yolks with the sugar until it has dissolved. Add the cornstarch and flour and whisk to incorporate, then add a ladle of hot milk to loosen up the mixture
Remove the lemon peel and add the egg mixture to the milk. Whisking all the while, cook the custard until it has reached a thick, velvety, pudding-like texture
Remove the lined baking tray from the fridge; pour in the hot custard to a 2cm depth and and spread it out with a spatula. Allow the custard to come to room temperature
Once the custard has cooled and hardened a little, cut into squares or diamonds. Dip them into the beaten egg and then roll them in the breadcrumbs
Heat up the sunflower oil in deep-fryer or pan to 180°C and fry the breaded custard squares until golden on all sides
Drain with a slotted spoon and carefully place on kitchen paper to absorb any excess fat. Serve immediately
