1 large egg yolk
1 tablespoon rice vinegar
1 teaspoon Dijon mustard
1 teaspoon sugar
1/2 teaspoon salt
1 cup neutral oil
1 to 2 teaspoons water, as needed
Whisk egg yolk, rice vinegar, Dijon mustard, sugar, and salt until smooth
Very slowly drizzle in the oil while whisking constantly
Continue whisking until thick and creamy
Add water a little at a time if needed to thin
Taste and adjust salt or sugar if desired
Refrigerate in a sealed container