Cooking the leaves and stems separately allows this dish a variety of texture and ensures that the leaves don't get overcooked.
Remove the stalks from the leaves: Hold the leaf in one hand, and gently pull out the thick stalk with the other. Cut the stalks into 2-inch-long pieces. Stack the leaves, and cut them crosswise into 4-inch-wide strips.
Heat the olive oil in a large skillet set over medium-low heat. Add the garlic, and cook just until golden. Remove and reserve the garlic. Add the stalks. Cook, stirring, 2 to 3 minutes to soften slightly. Add 3 tablespoons water, cover, and steam until firm but tender, 4 to 6 minutes.
Add leaves, cover, and cook until wilted, about 3 minutes. Sprinkle with the reserved garlic, and season with salt and pepper. Serve warm.