Add the mustard, Balsamic vinegar, water, basil and sun dried tomatoes to a blender. Blend for about 30 seconds until the mixture is smooth. Turn motor off and scrape down the sides.
With the blender on low, slowly pour the olive oil into the vinaigrette for about 10-20 seconds until it's well emulsified. If the consistency is too thick, add 2-3 more tablespoons of water to thin it out a bit.
Season with salt and pepper.
Transfer vinaigrette to an airtight container or mason jar with a lid and refrigerate for up to 1 week.
