Season chicken thighs with salt and pepper on both sides.
Melt 1 tablespoon of butter in a large pot over medium-high heat. Place the chicken thighs skin-side down and sear for 3-4 minutes until golden brown. Remove the chicken and set it aside.
In the same pot, melt the remaining 2 tablespoons of butter. Add diced onion and sauté for 2-3 minutes until soft. Then add diced red bell pepper, minced garlic, and tomato paste, sautéing for another 2-3 minutes until fragrant.
Stir in paprika, salt, and pepper. Pour in chicken stock and bring the mixture to a simmer.
Return the chicken to the pot, skin-side up. Reduce heat to medium-low, cover, and simmer for 20-25 minutes, turning the chicken halfway through cooking to ensure even cooking.
In a small bowl, mix flour and sour cream. Ladle out ½ cup of the cooking liquid and whisk it into the sour cream mixture to temper it.
Stir the sour cream mixture back into the pot, ensuring it blends smoothly. Cook for another 2-3 minutes to thicken the sauce.
Add chicken back to the sauce, spooning it over the chicken to coat.
Garnish with freshly chopped parsley and serve with spaetzle, egg noodles, or roasted potatoes.
