This is the gold standard of salad dressings: a perfect blend of oil and acidity. Try with: leafy greens, boiled leeks, artichokes.
Combine shallot, vinegar, mustard, and salt; let stand 15 minutes.
Add oil in a steady trickle, whisking constantly, until emulsified. Whisk in remaining oil in a steady stream.
To store, refrigerate, covered, up to 2 days.