Fish Stew with Herbed Toasts

Heat broiler with rack 8 inches from heating element. Melt 2 tablespoons butter in a large ovenproof skillet over medium-high heat. Add carrots, celery, 3 tablespoons shallot, and 3 thyme sprigs; season with salt. Cook, stirring occasionally, until vegetables are golden in spots, about 5 minutes. Stir in tomatoes and juice; simmer, breaking up tomatoes into bite-size pieces, until liquid is mostly evaporated, about 5 minutes. Stir in clam juice and fish; return to a simmer. Remove from heat.

Spread remaining 2 tablespoons butter over bread. Sprinkle with remaining 1 tablespoon shallot and thyme leaves from 2 sprigs; season with salt and pepper. Place atop fish. Broil until fish is just cooked through and bread is toasted, about 2 minutes (if bread is darkening too quickly, move skillet to lower rack); serve.