Season chicken on one side with salt, pepper and hot paprika.
In a large skillet over medium-high heat, add 2 tbsp. butter and oil. When hot, working in batches, add thighs, seasoned side down. and then season the top with salt, pepper, and hot paprika. Cook for 2 to 3 minutes per side or until golden brown. Transfer to a plate and set aside.
Reduce heat to medium and add the remaining 1 tbsp. butter. When melted, add onions, carrots, and celery: season with salt. Sauté for 3 minutes. Add red peppers and sauté for 2 minutes.
Add mushrooms, and stir to coat in fat: season with mixed peppercorns. Cover and sweat the veggies for 2 minutes.
Add garlic and quickly sauté for 30 seconds.
Stir in flour and cook for 1:30 to 2 minutes, stirring constantly.
Pour in white wine and cook until the liquid is almost gone, about 3 to 4 minutes.
Add chicken broth and Herbes de Provence. Increase the heat slightly to medium-high, and bring the mixture to a gentle boil; simmer for 5 minutes. Pour in heavy cream, bring to a simmer, and return the chicken pieces, including any accumulated juices.
Push the thighs into the sauce, making sure they’re entirely covered, reduce heat back to medium, and cook for 10 minutes or until the internal temperature reads 175ºF.
Sprinkle on fresh chopped parsley and serve over mashed potatoes.