Pat dry chicken thighs with a paper towel, then season with salt and cajun seasoning. Mix together flour, paprika, cayenne, white pepper, granulated onion and garlic powder.
Dredge the seasoned chicken in flour mixture on each side until coated. Shake off excess flour. Heat oil in a cast iron or skillet over medium-high heat; then fry chicken on both sides until golden brown — about 4 to 5 minutes per side or until browned.
Remove chicken from skillet and place on a plate. Add onions to the skillet, then saute for about 2-3 minutes . Then add garlic, thyme and continue cooking for 3-5 more minutes , stirring occasionally to prevent any burns or until onions is wilted. Remove onions and set aside.
Add butter to the pan , let it melt . Then throw in the seasoned flour left over from dredging the chicken to the skillet and stir with a wooden spoon until it comes together and forms a paste.
Slowly whisk in the chicken broth, followed by milk making sure there are no lumps; stirring and scraping the pan well,until it is incorporated. Mixture is slightly thicken — about 5 minutes. Return wilted onions back to the skillet , Thoroughly mix , season with salt.
Add browned chicken back to skillet, together with its juice that form on the plate to the skillet. Bring to a boil, then reduce heat to a simmer.
Slowly cook for about 30- 45 minutes or more, stirring occasional to prevent any burns. Adjust seasonings to taste.
Garnish with parsley, Serve with mashed potatoes.