Add butter, andouille sausage, and minced bacon to a heavy-bottomed Dutch oven over medium-low heat. Stir occasionally until bacon begins to brown but isn’t yet crispy. Turn heat to high and add onions, celery, and bell pepper. Sauté until fragrant (about 5 minutes). Add garlic and sauté another 2 minutes. Add canned tomatoes (carefully, as they may spatter). Stir and cook until sauce begins to darken and caramelize. Add chicken stock, bay leaf, Cajun seasoning, salt, and a generous amount of cracked black pepper. Turn heat to medium and simmer until sauce thickens, about 10 minutes. If you like, remove from heat and mix in 1 teaspoon of gumbo filé powder for an extra-sweet, earthy flavor.