Add the egg yolks, lemon, salt and pepper to the Thermomix bowl.
Close the lid, cover with the MC and bring speed to 4, 70 degrees celsius and for 4 minutes.
Slowly, slowly drizzle the ghee into the Thermomix bowl, and at 2 minutes, reduce speed down to 3 for a further 30 seconds to a minute. The longer you cook the sauce for, the thicker and firmer it will go, so you can stop here and examine the mix to see if it has reached your preferred consistency. If it has, just stop the cooking process, and serve.
The mix is best served immediately if possible, otherwise set aside and warm in the Thermomix on speed 2 or 3 when ready to serve.
If it is too thick, add a little water.
Bring a small pot half filled with water to the boil (ensure it is one you can place a glass or stainless steel bowl on top of later).
Reduce the heat so the water is only just simmering.
In the glass or stainless steel bowl, add all the ingredients apart from the ghee and whisk until combined.
Place on top of the pot so it begins to heat. Make sure the water doesn’t touch the bowl.
Slowly, slowly add the ghee whilst continuing to whisk the mix gently, just like you would with mayonnaise.
Once creamy and well combined, remove from the heat. If it is too thick, add the water to loosen it a little.
Serve immediately if possible, or warm through on a low heat whilst stirring when ready to serve.