Make sure all the ingredients are at room temperature. Add everything to a wide mouthed jar. Use less vinegar for a more mild mayo. 3 tsp (1 Tbsp) will make it nice and tangy!
Blend with an immersion blender. Don't move the blender for 15 - 20 seconds. Slowly move the blender up after this time, you can slowly move it up and down to emulsify everything. You will only need to blend for about 30 seconds or so.
Taste and adjust for seasoning. If it's thick enough, use right away or store in the fridge overnight to thicken. Should be good for about 2 weeks!