Steps
1. In a small bowl, whisk together the egg yolk and mustard until smooth.
2. Gradually add the vegetable oil in a thin stream while whisking continuously to emulsify the mixture.
3. Stir in the water, sugar, salt, and vinegar until all ingredients are well combined.
4. Adjust seasoning with additional salt or sugar if needed.
5. Serve immediately or refrigerate in an airtight container for up to 2 days.