Alice Waters writes in her book, The Art of Simple Food:
Cut off the leafy tops and fibrous stalks and trim off the root ends from the fennel bulbs. If you want, save some of the feathery leaves to chop and use later to garnish the dish before serving. Peel away any bruised outer layers. Cut the bulbs in half and then slice fairly thin. Heat a heavy skillet over medium-high heat. Pour in enough oil to coat the bottom generously and add the cut fennel. Let the fennel brown for a few minutes undisturbed. Start tossing or stirring occasionally and continue to cook until the fennel is tender. Season with salt, fresh-ground black pepper, and the chopped fennel leaves. Finish with a squeeze of lemon juice or a pinch of dried chile flakes.