01 - Pat chicken thighs dry thoroughly. Season on all sides with salt, black pepper, smoked paprika, and dried thyme.
02 - Heat olive oil and unsalted butter together in a large skillet or Dutch oven over medium-high heat until shimmering. Arrange chicken thighs skin-side down in a single layer. Sear until skin is golden brown, about 6 minutes per side. Transfer chicken to a plate and set aside.
03 - Add sliced yellow onions to the same skillet. Cook, stirring occasionally, until onions are very soft and deeply golden, about 8 minutes. Add minced garlic and cook for 1 minute more until fragrant.
04 - Evenly sprinkle flour over the cooked onions. Stir continuously, cooking for 1 to 2 minutes until the raw taste of flour dissipates.
05 - Slowly pour in chicken broth while whisking to blend smoothly and prevent lumps. Allow the mixture to come to a gentle simmer.
06 - Nestle seared chicken thighs back into the skillet, skin-side up. Spoon onions and gravy over the thighs for even coverage.
07 - Cover the skillet and reduce heat to low. Simmer for 25 to 30 minutes, or until chicken is completely cooked through and gravy is rich and thickened.
08 - Taste the gravy and adjust salt or pepper as needed for balance.
09 - Transfer chicken to serving plates. Spoon generous ladlefuls of onion gravy over each piece. Garnish with chopped fresh parsley if desired.