You will need a stick blender to make the mayonnaise from scratch. (If you dont have one, skip the next two steps and use 1 cup of store bought mayonnaise.)
In a measuring cup or the cup that came with the stick blender, add the egg (at room temperature), mustard seeds, lime juice, salt, and white vinegar. Finally add the oil and let it set so that oil is on the top layer.
Put the stick blender into the cup and press it down on the bottom and turn it on, leaving it on the bottom for 10-20 seconds. You should start to notice the mayonnaise forming. Once it starts to get thick, slowly elevate the stick blender to the top to incorporate all of the oil.
After the mayonnaise is made, add the cilantro, lime, salt and garlic (using a garlic press) and mix.
Serve and enjoy!