Melt Butter: Heat water, milk, salt, sugar, and butter in a pot until the butter melts and the mixture boils.
Add Flour: Pour all the flour into the boiling mixture and stir vigorously for 2-3 minutes until the dough becomes glossy and a film forms on the pot's bottom.
Cool Dough: Transfer the dough to a mixing bowl and let it cool for about 10 minutes.
Prep Eggs: Crack eggs into a separate bowl and whisk them.
Mix Dough: Use a hand mixer on low speed to mix the dough, gradually adding eggs. Start by adding half the egg and mix until fully incorporated, then repeat with half of the leftover egg mixture. Do the V-shape test by letting some dough slowly fall off a spatula or whisk and checking if it forms a 'V' shape. If the dough isn't there yet, continue adding the eggs bit by bit until it is.
Ready to Use: The dough is now ready for piping, baking, or deep frying.