Home-made mayonnaise is much better for your health than shop-bought and if you have a stick blender it is super easy and quick to do.
You can also use extra-virgin oil or avocado oil (or a mix) but these will have more impact on the flavour, which you may not like.
1 cup of cold-pressed (this is important) rapeseed oil
1 heaped teaspoon of Dijon mustard
0.5 tsp of salt (not table salt)
1.5 tbsp of apple cider vinegar
1 clove of garlic
Crack the egg into a tall beaker (the one that comes with a stick blender).
Pour in the oil and add all the other ingredients.
Place the stick blender on the bottom of the beaker and switch on and hold it still for 20 seconds. You will see the mayonnaise form and seep through the gaps of the blender. When most of the contents has turned to mayonnaise (this only takes around 20 seconds), lift the stick blender (still switched on) slowly to incorporate the remaining oil into the mayonnaise. That's it, super quick and easy :)