Cook pasta in salted boiling water and cook according to packet instructions.
Heat oil in a large pan over medium heat; add chopped mushrooms and fry for around 5 minutes.
Stir harissa paste, ketchup, cream, milk, hot pepper sauce, salt and pepper into the mushrooms; simmer over low heat, stirring occasionally. If the sauce gets a little dry, add a dash more milk or water. Add grated cheese if using and stir well.
When pasta is ready the mushroom mixture should be ready too. Drain pasta and serve with sauce on top. Enjoy!