500 g red onions
4 tablespoons olive oil
½ teaspoon Marmite
1 teaspoon plain flour
350 g penne
25 g butter
Parmigiano Reggiano cheese
1 Peel and very finely slice the onions, then add to a lidded frying pan over a medium-low heat with the oil and a little sea salt.
2 Turn down the heat to very low and cook for 10 minutes, or until the onions are soft, but not coloured, stirring frequently.
3 Stir in the Marmite and cook for another 1 to 2 minutes. Add the flour, mixing it in thoroughly, then pour in 100ml of boiling water.
4 Keep stirring until it’s simmering, then put on the lid and simmer over a very low heat for 30 to 40 minutes, or until reduced, stirring often.
Add a few tablespoons of hot water if it becomes too dry, and season to taste.
5 Cook the penne according to the packet instructions. Drain well, add to the onion sauce and cook for 1 to 2 minutes. Turn off the heat and stir in the butter until melted.
6 Finely grate over the cheese, then serve.