Remove excess fat from the chicken pieces. Rub a generous amount of the Magic Seasoning Blend on both sides of each piece, making sure each is evenly covered. Let stand at room temperature for 30 minutes.
Meanwhile, in a medium-size bowl combine the onions, bell peppers and celery, set aside. Thoroughly combine the flour with 1 tablespoon of the Magic Seasoning Blend in a paper or plastic bag. Add the chicken and shake until pieces are well coated. Reserve ½ cup of the flour.
In a large skillet (preferably not a nonstick type) heat 1½ inches oil until very hot (375º to 400º). Fry the chicken pieces until crust is brown on both sides, about 5 to 8 minutes per side; drain on paper towels. Carefully pour the hot oil into a glass measuring cup, leaving as many of the browned particles in the pan as possible. Scrape the pan bottom with a metal whisk to loosen any stuck particles, then return ½ cup of hot oil to the pan. Place pan over high heat. Using a long handled metal whisk, gradually stir in the reserved ½ cup flour. Cook, whisking constantly, until roux is dark red-brown to black, about 3½ to 4 minutes, being careful not to let it scorch or splash on your skin.
Remove from heat and immediately add the reserved vegetable mixture, stirring constantly until the roux stops getting darker. Return pan to low heat and cook until vegetables are soft, about 5 minutes, stirring constantly and scraping the pan bottom well. Set aside.
Place the stock in a 5½-quart saucepan or large Dutch oven. Bring to a boil. Add the roux mixture by spoonfuls to the boiling stock, stirring until dissolved between additions. Add the chicken pieces and return mixture to a boil, stirring and scraping pan bottom often. Reduce heat to a simmer and stir in the andouille and garlic. Simmer uncovered until chicken is tender, about 1½ to 2 hours, stirring occasionally and more often toward the end of cooking time.
When the gumbo is almost cooked, adjust the seasoning if desired with additional amount of Magic Seasoning Blend. Serve immediately.