1/4 cup grapeseed oil or mild, extra virgin olive oil
In a medium bowl, whisk together the vinegar, shallot, and salt. Let sit for 5 minutes.
Whisk in the mustard and pepper. Whisking constantly, add the oils in a slow, steady stream. Whisk again just before serving. Store in an airtight container in the refrigerator until needed and for up to 4 days.