Put the garlic on a wooden chopping board, coarsely chop then sprinkle with the sea salt and crush to a smooth paste using the flat part of a knife. Place a bowl on a wet tea towel (dish towel) that has been folded in half, then in half again — this stops the bowl flying off the bench. Put the egg yolks in the bowl, add the mustard and garlic paste and gently blend together using an egg whisk.
Add the extra virgin olive oil and sunflower oil, a few drops at a time, whisking continuously. Each addition of oil needs to be emulsified into the egg mixture before you add any more. Look for a change in consistency — it should become gradually thicker. Keep whisking, slowly adding the rest of the oils until you end up with a thick mayonnaise.
Check for seasoning. Season with the lemon juice and, if necessary, extra sea salt by dissolving the salt into the lemon juice before adding to the mayonnaise. This will avoid white salt spots developing in the finished mayonnaise.
Finally, whisk in