1.Wash chicken well. Boil until tender. Debone chicken, remove skin, cut flesh into small pieces and set aside. You can use leftover boiled chicken. Boil fettuccine and drain.
2. Meanwhile, in a non-stick medium saucepan, heat and stir 1 ½ tbsp butter and mushrooms for 5 minutes. Remove from pan and set aside.
3. In the same saucepan, add remaining butter, then add flour and stir for 30 seconds.
4. Remove from heat, add milk gradually and stir until there are no clumps. Return to heat, add water or broth and stir until mixture boils.
5. Add chicken, mushrooms, salt and pepper. Reduce heat and simmer for 5 minutes. Add double cream and stir. Add fettuccine and stir to mix all ingredients well. Serve immediately.
Don't boil pasta and set it aside till you make the sauce. While boiling it, prepare sauce so that you drain it and add it to the sauce right away. Pasta is always at its best when it has just been boiled and drained.