Season both sides of the chicken thighs with ½ teaspoon salt and ½ teaspoon black pepper.
Add the flour to a medium bowl and dredge the chicken on both sides, shaking off the excess flour. Reserve the leftover flour.
Heat the butter and vegetable oil in a large cast-iron skillet over medium-high heat.
Add the chicken thighs and cook for 3 to 4 minutes per side until golden brown and crispy.
Remove the chicken from the skillet and set aside while keeping the drippings in the pan.
Add the sliced onion to the skillet and cook for about 5 minutes until softened.
Stir in the garlic and cook for another 30 seconds.
In a small bowl, combine 3 tablespoons of the reserved flour with poultry seasoning, paprika, and ½ teaspoon each salt and pepper.
Sprinkle the flour mixture over the onions and garlic, stirring well.
Slowly pour in the chicken broth and milk while stirring constantly until smooth.
Return the chicken thighs to the skillet and nestle them into the gravy.
Bring the mixture to a gentle boil.
Cover the skillet, reduce the heat to low, and simmer for 20 minutes or until the chicken reaches 165°F internally.
Garnish the Southern Smothered Chicken Thighs with fresh parsley and serve over hot cooked white rice with plenty of gravy.