Set the oven to 180 C/ 350F. You will need an oven proof pot with a wide bottom and sides that aren't too high.
Pell and dice the onion. Crush the garlic and set it aside
Put the paprika, dijon mustard and sour cream in a bowl and gradually stir in the stock.
Put the 1/2 cup of flour into a bowl. Roll the chicken pieces in the flour. Empty the flour and set the bowl aside.
Heat the oven pot over medium-high heat. When nice and hot add the olive oil and fry the chicken skin side down first. Turn over after several minutes and when golden. Take the chicken out of the pan and put it onto the bowl set aside.
Pour off a little of the oil. Leave a small amount to saute the onions in ( or add a glug more olive oil). With the heat on medium, add the onions and garlic in the pot and stir until fragrant and just soft. Add the mushrooms and stir until starting to soften (and they will shrink down). Add the extra tablespoon of flour and stir well.
Pour in the sauce mix and stir well. Put the chicken on top skin side up. Put the pot into the oven
Roast the chicken for 35 minutes. Take out of the oven and either put a thermometer into the thickest part of the chicken. It needs to be just over 65F. If you don't have a thermometer pierce the thickest part of the chicken with a knife to make sure the juices run clear.
Now you are ready to serve the chicken with rice or pasta or couscous