Preheat a Dutch oven over medium heat first and then add some oil.
Season the chicken with some salt and pepper on all sides.
Sear chicken for a couple of minutes on each side until nicely golden brown. Sear the chicken in batches so you don't overcrowd the pot. Take chicken out and set aside.
Cooking chicken:
Add butter to the Dutch oven and add sliced onions. Mix in butter and let onions cook until completely softened and start to brown.
Move onions aside and add garlic. Cook until garlic is fragrant and mix it into the onions.
Mix in paprika and return the chicken to the pot, fitting it in as evenly as you can.
Carefully pour in chickens stock, making sure the chicken is covered, and stir to mix.
Bring the mixture to a simmer and lower the heat to low. Cover the Dutch oven with a lid, leaving a small crack for the heat to escape.
Cook chicken for 20 minutes and take off the lid. Carefully stir the chicken and liquids and cook another 15-20 minutes uncovered.
Finishing the sauce:
Make the roux by combining softened butter and flour. Mix it until it forms paste.
Stir in the roux into the pot and continue to slowly stir while it gently simmers and thickens, about 3-5 minutes.
Stir in sour cream and heavy whipping cream, cook about a minute, and take the pot off heat.