There are so many recipes out there for combining yoghurt/tahini/lemon that I can't claim to have reinvented the wheel here. However, this is the combination that I have found works every time ... the main thing is not to "round" out your tablespoons of tahini ... notice that I mention "level" tablespoons. Tahini has a very strong flavour and is tempered well with yoghurt and lemon juice, but if you use too much it can overtake the other ingredients which is not going to be to everyone's liking. I also use "hulled" tahini which is milder in flavour. Tahini can also fall into the "allergy" category (like it does for my son Sam who is allergic to sesame seeds) ... so if I am going to be serving it to him I replace the tahini with extra virgin olive oil which still gives a lovely flavour and a nice consistency to the sauce. You will find the tahini or olive oil will thicken up the yoghurt whilst it sits in the fridge so that is why I specify not to use Greek yoghurt to start with ... if that is all you have then make the sauce as per the instructions, then thin it down to a "dolloping consistency" with a little milk or filtered water ... don't be tempted to use too much lemon juice otherwise the balance of flavours will be out. Taste for seasoning with the sea salt and pepper, and use as much as you need to as it is an important addition to this sauce.