Combine flour, sugar, and salt in a mixing bowl.
In another bowl, whisk together eggs, milk, water, melted butter, and vanilla extract.
Gradually add the wet ingredients to the dry mixture, whisking until smooth.
Heat the marquesita iron or crepe pan over medium heat.
Grease it lightly with butter.
Pour a small ladle of batter onto the iron and spread it evenly to create a thin layer.
Cook until the edges start to crisp up and flip it over.
Add your chosen filling(s) while it's still hot.
Roll up the marquesita and let it cool slightly before serving.