So easy:

- 1 egg yolk in mason jar

- Add some vinegar, sugar, lemon, mustard, salt and pepper

- Put immersion blender in and add water til it touches blade

- Gently put oil, 1:4 olive & canola I find is delicious

- Activate blender and slowly pull up. Should form an emulsion almost immediately.

Better mayo than you'll ever get at the store