In a bowl, mix the ketchup, mustard, flour and Worcestershire Sauce. Mix it well and reserve.
In a pan on medium-high heat, melt the butter. Add the chicken and stir fry it. When the chicken is seared, add the salt and black pepper. Mix it well. Cook it for about 4 minutes.
Add the chopped onion and stir fry it for 2 minutes. Add the garlic and stir fry it for another minute.
Careful to not dry the chicken by over cooking it. Once the chicken water is mostly dry, remove the chicken from the pan and reserve.
Add the cognac to the pan and bring it to a boil until the alcohol had evaporated. It will take around 1 minute. Add the mushrooms to the pan and cook it for about 2-3 minutes.
Put the chicken back into the pan, together with the sauce from the bowl. Mix it well and cook it for a minute.
Add the cooking cream and cook it until the sauce boils.
Serve it on top of rice or pasta, with a side of salad.