Cook the spaghetti in salted boiling water as per packet instructions and keep aside.
In a pan, heat the olive oil and add the grated garlic followed by the mushrooms. Stir fry on high heat and season the mushrooms with salt and chilli flakes. Keep aside.
In the same pan, melt butter and add the mascarpone cheese. Mix well; add the milk to loosen up the sauce followed by the Parmesan. Season with salt and black pepper; cook till all the ingredients are combined to get a smooth sauce. Add the spaghetti, mushrooms and parsley; toss well to combine.
Serve hot with chopped parsley, crushed walnuts and grated parmesan.