Place the milk, butter, sugar, salt and water in a medium saucepan over a medium heat. Stir until the sugar has dissolved and the butter has melted. Bring to a gentle boil and remove from the heat. Tip in all of the flour (160g) stirring vigorously with a wooden spoon until well combined.
Return the saucepan to the heat and keep stirring the mixture for another 2- 3 minutes until you notice a thick film forming at the bottom of the saucepan. The mixture should be very thick, smooth and shiny, with no visible lumps.
Transfer the dough into a bowl of a standing mixer, spread it into a thin layer over the sides and the bottom of the bowl with spatula and allow the mixture to cool for about 15 minutes, until it is room temperature.
Fit the mixer with paddle attachment, scrape the sides of the bowl with spatula and add two beaten eggs into the dough. Start mixing it on a medium speed, until the eggs are well incorporated. You may have to scrape the sides of the bowl every now and then.
Add the third egg into the dough, and again, mix on a medium speed until fully incorporated. Scrape the sides of the bowl as necessary. Add the egg white and lemon zest and stir again on medium speed until fully incorporated. Transfer the dough into a large piping bag fitted with large open star nozzle and place it in the fridge for at least an hour.
Half fill a deep-fat fryer or heavy based large saucepan with vegetable oil and heat it up to 180°C. Make sure the oil temperature stays constant at all times of frying the doughnuts.
Cut parchment paper into 12 squares, each 9 x 9 cm. Draw a circle 7cm in diameter onto each square. Turn each paper square over, so that the drawn circle is on the underside. Hold the piping bag vertically, over one of the parchment squares, and start piping an even circle of dough, just making the ends to meet and connect. Repeat with the remaining dough and parchment squares.
Gently, place the cruller in the hot oil, with the parchment paper still attached to it and facing up (although, it's fine if the parchment paper detached itself from the cruller when placing it in the hot oil). Alternatively, place the square of parchment with choux ring on it onto a slotted spoon and carefully lower it into the hot oil.
Fry the doughnuts about 2- 3 at the time for about 2-3 minutes on each side, removing the parchment paper with metal tongs. They should be deep, golden brown on both sides. Remove the doughnuts from the pan using a slotted spoon and place on a large plate lined up with some kitchen paper. Allow the crullers to cool down before glazing.
For the glaze:
Mix all of the ingredients together, adding enough milk to create runny, but also thick enough glaze that will cover the doughnuts. Dip the doughnuts into the glaze & enjoy!
Notes
Using the strong white flour in choux pastry will make sturdier crullers, which are less likely to collapse after frying.
Chilling the dough for at least an hour makes it much easier to work with. It will also help to prevent the doughnuts from splitting, while frying them.
Keep an eye on the oil temperature at all times, make sure it doesn't exceed the 180° C mark.
The choux pastry can be made up to 2 days ahead and stored in the fridge.
To bake (instead of deep frying): Heat the oven to 220°C (fan) and place the crullers on a baking tray, leaving 3-4 cm space between each doughnut. Place the tray with doughnuts in the hot oven and bake for 5 minutes, then reduce the heat to 160°C (fan) and bake for another 15 minutes. Turn the heat off, open the oven door slightly and allow the crullers to sit in the oven for another 10 minutes. Remove from the oven and dip them in glaze.
Doughnuts are best served and eaten on the same day they are made.
Store any leftover crullers in the airtight container at room temperature for up to two days.
Freezing instructions: Freeze piped choux rings on a baking tray until frozen. Transfer to a freezer friendly bag or container and keep in your freezer for up to a month. Thaw them slightly while your oil is heating up. Add couple of minutes to frying times, if cooking from frozen.