-
1
Chop enough fennel fronds, if using, to measure 2 tablespoons.
-
2
Quarter fennel bulbs lengthwise, then cut lengthwise into 1/4-inch-thick slices.
-
3
Cook fennel bulbs, sliced onion, and anchovy paste in 1 1/2 teaspoons oil in a 12-inch heavy nonstick skillet over moderate heat, stirring, until coated, about 1 minute.
-
4
Season with salt and pepper, then add broth and braise, covered, stirring occasionally, until vegetables are tender, about 20 minutes.
-
5
Remove lid and boil, stirring occasionally, until liquid is evaporated, about 10 minutes.
-
6
Transfer fennel mixture to a 1 1/2-quart shallow gratin or other shallow 9-inch ceramic or glass baking dish.
-
7
Preheat oven to 450F.
-
8
While fennel mixture is braising, cook chopped onion, red pepper flakes, and salt to taste in remaining teaspoon oil in an 8-inch nonstick skillet over moderate heat, stirring occasionally, until onion is softened, 3 to 4 minutes.
-
9
Add tomatoes with juice and simmer, breaking up tomatoes with a spoon and stirring occasionally, until very thick, 15 to 20 minutes.
-
10
Arrange fish fillets on top of fennel mixture and season with salt.
-
11
Spoon tomato sauce over fish.
-
12
Cover with a sheet of parchment paper or wax paper, then cover baking dish tightly with foil and bake in middle of oven until fish is just cooked through, 20 to 25 minutes.
-
13
Sprinkle with fennel fronds.
