Rinse and dry chicken throughly. Remove skin from chicken and sprinkle black pepper, seasoned salt and garlic powder on both sides. In a large pan or dutch oven, heat 1 tablespoon of olive oil and lightly sear the chicken. Remove the chicken and set aside.
In the same pan, add the remaining olive oil, onions and celery and cook until soft. Add the butter and let melt over medium heat. Use a wire wisk and slowly wisk in the flour until a paste is formed. Slowly add the water and wisk until well mixed. Add the rosemary and thyme and mix well.
Place the chicken in a baking pan, pour the gravy over the chicken, cover with foil and bake in a 350 degree oven for 45 minutes.
Remove the foil and baste the chicken in the gravy before serving.