Once the water is cooking, you can add the pasta. Cook this following the package instructions.
Heat the olive oil in the sauce pan and bake the onions until soft and glossy. Add the madeira and, if you like, some thyme leaves and stir again.
Then you can add the cream, the crumbled mushroom stock cube and the rambol cheese. I prefer to add the rambol cheese per tablespoon so the cheese melts quicker.
Use a whisk to mix the sauce and to remove any lumps. Once the sauce is cooking, you can turn off the heat or turn it on low. You don't this sauce to cook for a long time. It just needs to be hot ;)
Once your pasta is cooked, you can drain it and add it to the sauce. Mix everything, check if you like the thickness of the sauce. Do you like the sauce to be a bit more fluid? Add some cooking water of the pasta.
Have a quick taste and add some additional salt&pepper (if you prefer)!