Heat the oil in a large frying pan over medium heat.
Saute the onions, mushrooms and red pepper until they begin to soften.
Add the garlic and cook for a moment or two.
Stir in the chicken stock, salt, pepper and paprika.
Bring just to the boil, stirring almost constantly, then reduce the heat and simmer with the lid off for five to ten minutes.
Meanwhile, cook the pasta according to package directions.
Preheat the oven to 350°F (175°C or 160°C for a fan oven).
Combine the flour and crème fraîche in a small bowl, mixing until smooth.
Stir the flour and crème fraîche mixture into the ingredients in the frying pan.
Bring the mixture in the frying pan just to the boil once again, stirring constantly.
Cook and stir for a moment or two until thickened.
Stir in the cooked chicken pieces.
Drain the pasta and transfer to a large casserole dish.
Grate the nutmeg into the chicken sauce in the frying pan.
Taste the sauce for seasoning, adding more salt and pepper if necessary.
Pour the sauce over the pasta in the casserole dish and stir gently to combine.
Cover the dish with foil or an oven-safe lid and bake for 15 to 20 minutes.
I like to serve this family style from the centre of the table. Be careful, the dish will be hot!