Whisk the base: In a small bowl, whisk together the vinegar, Dijon mustard, salt, pepper, and sugar until combined.
Add the oil slowly: While whisking constantly, slowly drizzle in the olive oil in a thin stream until the dressing is thick and emulsified.
Taste and adjust: Check the seasoning and add more salt or pepper if needed. If the dressing is too sharp, add another pinch of sugar.
