Preheat the oven to 170ºC fan-forced.
Place all three cheeses in the mixing bowl and chop 5 sec/speed 8. Set aside.
Pour the milk into the mixing bowl and add the onion, bay leaf and cloves. Infuse by heating 5 min/60ºC/Reverse/speed 1.
Pour the milk and flavourings into a jug and allow it to stand and infuse for a further 5 minutes or so.
Meanwhile, place the butter into the mixing bowl and melt 3 min/60ºC/speed 2.
Add the flour and cook 4 min/Varoma/speed 4. The mixture should be sizzling slightly and look a little sandy; if not cook a minute further.
Strain the warm milk back into the mixing bowl then cook 5 min/90ºC/speed 4. Then cook again 2 min/100ºC/speed 4, the mixture should be boiling at the end of the cooking time.
Take the lid off and allow the sauce to cool for a few minutes. Then add the grated cheeses, mustard and egg yolk. Mix 30 sec/speed 4.
Combine the sauce with the cooked macaroni and turn into a buttered 1-litre shallow ovenproof dish.
Bake in the centre of the oven at 170ºC (fan-forced) for 30−40 minutes, the sauce should be bubbling at the sides and the top nicely browned.
Serve with greens and crusty bread.
AND … Your call as to when to boil the macaroni. You can do it while the sauce is in the Thermomix so they’re ready at about the same time but if you cook the pasta first, give it a light coating of butter or oil as soon as it’s drained so it doesn’t form clumps while you’re waiting for the sauce to cook. Or, keep the finished sauce in the fridge for a day or three until you’re ready to boil the pasta and do the bake.