Heat a heavy duty 10-inch skillet over medium-high heat. Add one tablespoon olive oil and swirl it to evenly coat the pan. When the pan is hot, but not smoking, add the sea scallops to the pan flat side down. Sear the scallops for 2 minutes without touching or moving them. Adjust the heat if the pan is getting too hot. Turn the scallops over and sear for 2 minutes until the scallops are done. Depending on the size of your scallops will determine how long they need to cook. They are done when the center is opaque in the middle, and feel firm when pressed with your finger. When in doubt, cut a scallop down the center and check. The scallop won't go to waste, just add it to the salad. The scallops will continue to cook from the residual heat, but you want to remove them when they are just done.
* This is a light vinaigrette and not one to use balsamic vinegar. If you have a good quality red wine vinegar it is OK to use. I just have not found one I like, so I usually don't cook with red wine vinegar.
The vinaigrette makes about 1 cup / 250 ml so you will have plenty leftover. Store the vinaigrette in an air tight container in the refrigerator. The vinaigrette will taste better, and last longer, if you remove the shallots from the vinaigrette. Pour the vinaigrette over a fine mesh strainer into a container to catch all the shallots.
Discard the shallots and refrigerate the vinaigrette.
If you want to thoroughly emulsify the vinaigrette, it is easy to do with an immersion blender. The vinaigrette made with a blender will be thicker and heavier. I like this salad with a lighter dressing so I mix it by hand and not worry about the dressing being emulsified. It is your choice. Make the salad dressing as you prefer.