Heat the butter and bacon fat in a saucepan until foaming. Add the diced onion and shallot, cook, stirring often, over medium heat for 5 minutes. Toss the garlic, thyme and salt into the pan, cook for 5 more minutes. Add the sliced carrot and potatoes, cook, stirring often, for 5 minutes. Add the chopped tomatoe, white wine and 8 cups of water, bring to a simmer. Cook for 15 minutes skimming the surface occasionally until the potatoes and carrot are tender.

While the soup is simmering, seaon the catfish pieces liberally with salt and freshly ground pepper. When the potatoes are tender, add the catfish, parsley and scallions to the pot. Cook, partialy covered at very low simmer for 5 minutes. Taste and add more salt and freshly ground pepper as needed.