Add the aquafaba into a high-powered blender and blend until airy and white on medium speed. This takes about 30 seconds. Alternatively, add the aquafaba into a bowl or container and blend with a stick blender.
Now add the mustard powder, white wine vinegar and salt and blend for a few seconds.
Finally, while blending on a slower speed, slowly pour in the sunflower oil and let emulsify. Feel free to adjust the amount of oil added to make the mayo's consistency thinner or thicker.
Scarpe down the sides, give the mayo another quick blend. It's ready to use now.