Reduce heat under pan a little and add 2 tablespoons butter. Add peppers, onions and garlic to butter. Add 2 tablespoons flour and cook 5 minutes, stirring frequently. Season with salt, pepper and paprika, and stir in wine. Cook 30 seconds then add tomatoes and stock, and whisk to combine sauce. Slide reserved chicken into pot and reduce heat to simmer, medium-low. Cover pot and cook 15 minutes, turning occasionally.
Bring a pot of water to a boil for gnocchi. Boil gnocchi 3-4 minutes until they float to top of pan and drain well.
Heat remaining 2 tablespoons butter in a skillet over medium to medium-high heat. Add gnocchi, season with salt, nutmeg and add parsley. Cook 2-3 minutes, turning occasionally.
Add a couple of ladles of chicken sauce to a bowl and stir in sour cream. Add bowl contents back to the pot and gently stir to combine. Turn off heat.
Serve chicken topped with sauce and with gnocchi alongside.