Cut off and discard stalks from fennel bulbs, reserving fronds. Chop 1 tablespoon fronds and discard remainder. Cut bulbs lengthwise into 1/2-inch-thick slices, leaving core intact.
Heat oil in a 12-inch heavy skillet over moderately high heat until hot but not smoking, then brown fennel slices well, turning over once, 3 to 4 minutes total.
Reduce heat to low. Sprinkle fennel with salt and pepper, then add broth and water. Cook, covered, until fennel is tender, 10 to 12 minutes. Sprinkle with fennel fronds.