Cook the spaghetti in plenty of boiling salted water, according to the packet instructions.When the pasta is almost cooked, melt the butter in a small saucepan and add the Marmite and 1 tablespoon of the pasta water, mixing thoroughly to dissolve. Reserve ½ cup of pasta water; then drain the pasta and pour the Marmite/Vegemite mixture over the drained spaghetti, adding a little reserved pasta water to amalgamate if required. Serve with plenty of grated Parmesan cheese.