Place a large pot of water onto your cooktop and bring to the boil with the salt. Do not skip seasoning the water. It needs to cook into the pasta.
Cook the spaghetti noodles to al dente, following the package instructions on timing. Drain but reserve some of the pasta cooking water.
Meanwhile, place butter and ThermoMite (or go ahead and use vegemite to make it even easier) into the Thermomix bowl and melt 5 min/80°C/speed 3. Add a splash of the hot pasta water and blend 10 sec/speed 8.
Toss the noodles and sauce together and serve immediately with lashings of parmesan or other cheese of choice.