Add the pasta to a pan of boiling water, set to simmer and cook as per packet instructions (around 8-10 minutes).
Add a dash of oil to a frying pan and turn up the heat, add the red onion and sugar, turn down the heat to a low to temperature and cook the onions while stirring with a spoon to prevent sticking, until they have softened and are starting to go brown (caramelising). Remove the pan from the heat, add the balsamic vinegar (if using) and set to one side until the sauce and pasta are ready.
Place the brown onion and garlic in a frying pan with a dash of oil and cook on a low heat for around 5 minutes to soften.
Once the cauliflower has softened, place it in a large bowl with all the sauce ingredients (brown onion and garlic, steamed cauliflower, spices, seasoning, stock cube, boiled water and milk).
Check the temperature of the sauce and if you think it needs to be a little warmer, simply pop in a pan (use the frying pan to save on washing up!) and reheat for a few minutes before adding to your pasta.
Once the pasta is cooked, drain and place in the bowl with the sauce, add the caramelised onions, combine then split between 2 bowls for serving.