Dear Baf,

I have seen your issue with mayonnaise and found to recipes, one in the Germany Thermomix recipe book and one in the French one:

The German version

1 egg (the entire egg)
10 g (lemon juice)
1 teaspoon of mustard (medium hot)
1 pinch of pepper
1/4 tea spoon of salt
250 g of oil (rapeseed-, thistle- or sunflower oil)

Step 1:

Put egg, lemon juice, mustard, salt and pepper into the bowl.

Step 2:
Place measuring cup on Thermomix lid, speed up TM to 3.5 (if you are above 1'500 m/4'500 f increase speed a little). Now slowly let the oil drop onto the Thermomix lid and hold the measuring cup (so that the measuring cup does not move up and the oil slowly drops in). After the entire oil dropped in, use spatula to put the remaining oil of the lid into the bowl, after this the mayonnaise should be perfect.

At least with me it always worked.

The French version I never tried but here the recipe from the French book:

2 egg yolk
1 soupspoon of mustard
1 soupspoon of vinegar or lemon juice
2 measuring cups of sunflower oil
1 pinch of salt
Pepper

Step 1:

Insert the butterfly (whisk) into the bowl and add the egg yolk, the mustard, the vinegar (or lemon juice) the salt and the pepper

Step 2:
Set the Thermomix on 2min with speed 4 (remember with butterfly never over speed 4) and drop the oil slowly on the lid of the Thermomix without brakes.

I never tried this recipe and hope my French was good enough.