Smash up the garlic with the salt in a mortar and pestle (if you don't have a mortar and pestle you can very finely chop the garlic). Place the egg yolk and mustard in a bowl and whisk. Then start to add your olive oil bit by bit. Once you've blended in a half cup of the olive oil you can start to add the rest in larger amounts. When you've added it all, you can add the garlic and lemon (to taste) and any extra flavors such as basil, fennel tops, dill, chopped roast nuts. To finish just season to taste with salt, freshly ground black pepper and lemon juice.
Consumption of raw or undercooked eggs, shellfish and meat may increase the risk of foodborne illness.