Boil the pasta until it has cooked through (this should take about 12-15 minutes on a medium to high heat). Once cooked, drain and wash off the starch with cold water and leave to one side in some cold water until needed. Drizzle olive oil to prevent it from sticking together.
In a saucepan, heat the olive oil and add the finely chopped garlic, cook for 1 minute.
Add the onions, green chilli and crushed stock cube and cook for 3-4 minutes.
Add the mushrooms and cook for a further 4-5 minutes.
Finish this with the fresh coriander and leave to one side.
Mix together the water, cream and milk and leave this to one side.
In a sauté pan to make the roux (sauce), melt the butter.
Next whisk in the flour and mix for 30 seconds.
Add the cream, milk and water mixture and whisk until smooth, add the cheese and salt, cook for 30-40 seconds.
Add the mushroom mixture to the sauté pan, together with the drained pasta and garam masala.
Cook the pasta for a final two minutes in the sauce.