Preheat oven to 400F.
Rub the chicken with olive oil, season with salt and pepper. Fry the chicken, skin side down, in a pre-heated, ovenproof skillet. You just want to get the skin to a light golden brown. Now place in the oven for about 10 minutes to roast.
Remove pan from oven, remove chicken and spoon off all but 2-3 tsp of fat.
Gently fry the onions in the remaining fat until soft and translucent over medium to low heat - 5 to 7 minutes.
Now the tricky part. Add the paprika to the pan along with enough oil to keep the paprika wet and toast on absolute low for around 30 seconds. If you scorch the paprika even a little bit it will turn bitter. Have your chicken stock at hand to stop the frying instantly. It's your safety blanket. If this scares you (and it should), add a little drizzle of stock when you add the paprika and cook the resulting slurry for 30 seconds.
Add the stock - you want it about 1/4 inch deep in your skillet.
Return the chicken to the skillet and place in oven until the chicken reaches an internal temperature of 165F, around 15 to 20 minutes. Keep your eye on the liquid - you may have to add a bit more stock along the way.
Remove the skillet from the oven and set the chicken aside. Mix the flour into the sour cream mixture in a clean bowl until thoroughly combined.
Temper the sour cream mixture by adding a couple tablespoons of hot liquid from the chicken to the sour cream and stirring. Do it again. Next mix the tempered sour cream into the remaining liquid. Taste and adjust seasoning.
Serve chicken paprikash with sauce. It's works with almost any starch - potatoes, pasta, or fried gnocchi.