Cook the aubergine choosing any of the following methods
Putting it in a tray in the oven for about 10 minutes at 150 degrees celsius (Grill mode, not fan mode!). You'll need to flip the aubergine at around 6 minutes
Pre-heat a pan at medium fire, add the olive oil and then the aubergine for about 12 minutes, you'll need to flip the aubergine around 7 minutes from when you start
Cook the aubergine directly in the stove (not very recommended tbh!) but some people like doing it this way. It should take about 6 minutes at medium fire. Btw, you should remove the green part of the aubergine!
Roast the garlic/coriander in a pan for about 4 minutes or if you used the pan method, add it 4 minutes before you finish (it is not necessary to roast it! depends on your preferences)
You know the aubergine is ready when the aubergine is softened and golden brown.
Remove all the skin (it should come off easily). This step is optional! But take into account that making it with the skin will result in a purple-ish baba ganoush with a slightly earthy flavour (I like it, some people don't!). Also, notice that the purple skin is full of antioxidants, hence if you have a high-speed blender, I suggest that you blend everything and eat the whole food :)
Add all the ingredients (tahini, aubergine, salt, lemon juice, and coriander) to the blender or a food processor until smooth
Optionally, you can use a mortar and pestle and mix all the ingredients there