Put the pasta in a pan of salted, boiling water, stir briefly and cook for eight to 11 minutes, depending on how al dente you like it.
Meanwhile, if you’re making your own breadcrumb topping, melt a little butter (or a dash of oil) in a frying pan, then add the breadcrumbs and fry until golden and crisp. Tip out on to a plate.
Once the pasta is almost ready, scoop out a ladleful of the cooking water. Put the grated cheese in a heatproof bowl, then gradually whisk in just enough of the hot water to make a smooth, bechamel-like paste.
Melt the 25g butter in the breadcrumb pan and stir in the Marmite.
Drain the pasta well and toss it into the Marmite butter, along with the cheesy paste.
Transfer to a bowl and top with the breadcrumbs, if using. Chop the chives, if using, directly over the top, scatter over a little extra grated parmesan and serve.
