For the Choux Paste
Bring the milk, water, butter, sugar and salt up to a full simmer over medium high heat. Reduce the heat to low and stir in the flour with a wooden spoon, stirring vigorously until the dough “cleans” the sides of the pot (no longer sticks). Scrape this mixture into a large bowl and use electric beaters or a stand mixer fitted with the paddle attachment and beat on medium speed for a minute or 2 to cool it a little.
Break two eggs into a small dish and whisk them just to blend a little. Add these to the flour mixture while still on medium speed and mix until blended. Add the remaining 3 eggs one at a time and mixing well after each addition.
Work with this recipe while the batter is still warm.
For the Crullers
Fill a pot with oil so that it is about 2-inches deep, but comes up to only a third the height of the pot. Heat this to 170°C (use a candy/fryer thermometer to measure) or use a tabletop fryer following manufacturer instructions.
Fill a fabric (not a disposable plastic) piping bag fitted with a large star tip with the choux paste (you may have to fill in multiple batches). Pipe circles on small pieces of lightly greased parchment paper and gently slide them into the oil trying not to splash, removing the paper. You can also flip the piped crullers onto a slotted spoon and lower them into the oil.
Cook the crullers for about 5 minutes, turning them halfway through cooking. Lift the crullers out with a slotted spoon or straining spoon and place them on a paper towel lined plate to cool. Dust with icing sugar and serve immediately.