I use an immersion (stick) blender. I assume a regular blender would work just as well, and probably a food processor too.

Place soy milk, salt and mustard (if using) in blender jar.

Measure out oil and set aside ready for use. I measure out the maximum, and stop pouring (directions in step 5) when I reach the desired consistency.

Turn on blender on med-high and blend milk for 20-30 seconds.

While still blending, start pouring the oil slowly into the jar. After about ten seconds the mixture should begin to thicken.

Keep adding oil until you reach almost your desired consistency. You can make it anything from watery to very thick. The more oil you use, the thicker and creamier the final result.

Add the vinegar and keep blending until you're happy with the result.

Taste and correct if necessary. Blend again for a few more seconds if you do.

Options: This recipe is very versatile and can be turned into any mayo-based dressing. For example: Caesar salad dressing: add 1 minced clove of garlic, 2 tbs water and 1/2 teaspoon sugar. Aiole: add 2 cloves garlic and 1/2 tsp freshly squeezed lemon juice. Please share your own variations!

Keeps fresh for at least a week if stored refrigerated in an airtight container. May keep for longer, but I prefer making small batches more often.