In a heavy skillet, melt butter; sprinkle with flour & stir quickly to combine butter & flour evenly into a thick, smooth roux. Continue cooking, stirring often, as the roux turns from white to golden brown, about 2 minutes. Add spice blend, onion, green pepper, celery & garlic & stir quickly, mixing the vegetables into the roux. Cook until everything is fragrant & softened, 1-2 minutes more.