Place Dijon, vinegar, salt, pepper, shallot, and garlic in a bowl or jar.
Whisk together until combined.
Add olive oil in a slow, steady stream, whisking constantly to create an emulsion.
Taste and adjust: more vinegar for sharpness, more oil for mildness, more Dijon for body.
Add a tiny amount of sweetener if the vinegar is very sharp.
Dress salads immediately before serving — never let a dressed salad sit.
Store remainder in a sealed jar. Re-shake before each use.