Meanwhile, prepare the dressing. Add all of the ingredients to a high powered blender, such as a Vitamix, starting out with JUST 3/4 cup milk process until very smooth and creamy on high. If using canned coconut milk, make sure you have shaken the can really well first. Scrape the sides a couple of times and blend again for a good couple of minutes so it gets really smooth and thickens. The dressing will be fairly thin, but will thicken well in the fridge. Add more milk if you want it thinner.
Pour into a container and chill in the fridge for an hour or two to marinate, so it gets cold and thickens further. The flavor really is best after it chills and marinates (even better overnight!).
If making the potato salad, toss the potatoes with as much dressing as you like and chill for several hours for the dressing to absorb into the potatoes. When ready to serve, taste and add any more salt/pepper if needed. I like to add extra dill and freshly ground black pepper.