A great gumbo requires patience with the roux, a slowly browned mixture of oil and flour. When the color gradually deepens to a milk chocolate hue, you know magic is about to happen. If you’re tempted to rush, the flour burns and creates an acrid taste. But with the perfect roux, plus the depth of flavor brought by crab, trout, shrimp, crayfish and wild rice, this most famous of NOLA exports is transporting. Roux’s roux rocks.