Slice tautog into eight to twelve 2x2-inch chunks. Season each side of tautog chunks lightly with salt and pepper.

Heat 1 tablespoon oil in an enamel Dutch oven or heavy pot over medium heat. Add celery and fennel; cook until starting to soften, 3 to 4 minutes. Add onion and a splash of white wine; cook for 2 to 3 minutes. Reduce heat to medium-low, add garlic, and cook for 2 to 3 minutes.

Add tomatoes, remaining white wine, cumin, red pepper flakes, and a pinch of salt; stir to combine. Cover and cook until tomatoes begin to break down, 15 to 20 minutes.

Mash down tomatoes to break them up a bit. Add chorizo in a layer and top with fish chunks. Drizzle each chunk with remaining olive oil and add a small pinch of saffron to each. Sprinkle 1 tablespoon parsley over top. Reduce heat to low, cover, and cook until fish flakes easily with a fork, 12 to 15 minutes.

Spoon sausage and vegetable mixture into bowls and top with fish. Garnish with fennel fronds and remaining parsley.