In a tall glass mason jar or glass measuring cup, add the aquafaba, vinegar, mustard, syrup, and salt. Using an immersion blender on high speed, blend until all the ingredients are well combined.

Place the oil in a measuring cup with a pour spout. While the immersion blender is running on high, slowly stream the oil into the jar with the other ingredients. Blend for 1 to 2 minutes. Move the blender up and down toward the end to incorporate a little air. If the mayonnaise is too thin, stream in a little more oil to thicken and make the mayonnaise a bit more creamy.

Taste the mayonnaise and adjust the flavors to your liking by adding a little more vinegar, mustard, syrup, or salt.

Use immediately, or cover the jar and store it in the refrigerator for up to 2 weeks. Serve with sandwiches, use to make salads and dressings, or add to your favorite dipping sauce recipe that calls for mayonnaise.