Properly done, aioli is a great sauce but it requires really fresh ingredients to make well.
Ingredients (Serves 6)
2 or 3 fresh, fat garlic cloves, peeled and chopped
A large pinch of coarse sea salt
1 large very fresh egg yolk, at room temperature
Juice of half a lemon
150 ml rapeseed oil (preferably organic)
75 ml extra virgin olive oil - a nutty, golden one is best.
Freshly ground black pepper
Method
Place the garlic and salt into a food processor or blender and pulse for a few seconds. Add the egg yolk and lemon juice, and pulse on and off until well blended. Turn the machine on and begin adding the oil (rapeseed first, then olive) in a thin stream. If it becomes too thick, thin it out with some tepid water and continue adding the oil until you've used it all. Finish with the pepper.
The reason for using only 1/3 olive oil is to keep the flavour of the oil from becoming overpowering.