[this would have come in helpful for fighting vampires last night ....]
many mediterranean cultures have variations of this punchy garlic sauce. different versions include the provençal aïoli, the greek scordalia, and the catalonian allioli. there are also subvariations such as the french aillade.
to make this recipe you must have your mise-en-place ready. it can sometimes be a fussy sauce because of the oil & acid amalgamation. it is not the sort of thing you stop to go and ream your lemon and then measure oil.
in terms of preparation techniques, traditionally the thoum is made in a wooden mortar but it can be made the easier and faster way, in a blender or food processor, with the blender being a better choice. the sauce can be made with just garlic, lemon juice, salt and oil but this is an unstable mixture requiring skill at combining the oil with the garlic — a sometimes difficult procedure, especially for beginners. because of this, people will add a thickener like potato, mayonnaise or soaked bread which has been squeezed dry to bind it. i am showing you the easier way here today and will post the other method some time in the future. i suggest reading the whole recipe first before starting to decide how you want to proceed with it.
updated version *II* .
1 head of garlic, separated & peeled
1/8 c lemon juice [up to 1/4 c]
1/2 - 1 tsp kosher salt, not regular small grained
1/4 - 1/2 tsp sugar
1/4 c mild olive oil
1/4 c vegetable oil
1 very small floury potato OR
mayonnaise (LOTS) OR
bread soaked & squeezed dry
choose a small floury potato [not waxy, this is important], peel it and either microwave it or cook it in a small pot of boiling water. you may cut it in 4 pieces to cook faster. let it cool and set aside for use later.
separate all the cloves of the garlic, peel and place aside. measure out your salt, lemon juice and oil. put the oil in a pyrex type vessel that you can pour from.
in a blender, add the salt and garlic and process until very well ground. add your lemon juice. start with 1/8 c to begin with [if you would like it more sour, add another tablespoon or two at this point]. i add 1/4 - 1/2 tsp sugar to balance the lemon.
with the motor running on low, start to very slowly add the oil in a steady stream.
after about 1/4 c has been added, turn up the speed and continue adding the rest until all has been added. blend for about 20 seconds at high speed.
at this point, the thoum is ready to use. it will most likely be quite thin, especially if you used the 1/4 c of lemon. that is fine, it is a matter of taste and how you will use this. in its thin form, it can be used to roast vegetables, like potatoes, in the oven. if you want the restaurant type version continue with the next step. note that many of the restaurant versions are basically mayonnaise which heavily flavoured with garlic and some lemon juice. so, if that is what you are after, use mayonnaise to thicken the thoum. mostly likely you will need lots of mayonnaise to thicken this amount of garlic, oil & lemon juice so you may want to make only half as much as a trial.
it can be thickened two or three ways —
add half of the small potato and blend well about 30 seconds. test the viscosity. if you want it thicker, add the rest.
the other options are to use soaked and squeezed bread in small amounts or mayonnaise. the way we get it here where i live, it is more of a mayonnaise-y sauce which i don't not like. you choose how you like it. if adding mayonnaise, i suggest doing it carefully so as to prevent separation. you may want to blend it in with the garlic sauce by hand.
enjoy in modest amounts.