Cook Broccolini in a 3-quart pot of boiling salted water until stems are crisp-tender, about 5 minutes, then drain in a colander.

Heat 2 tablespoons oil in a heavy skillet over moderately high heat until hot but not smoking, then sauté half of garlic, stirring, until pale golden, about 30 seconds. Add half of Broccolini, 1/4 teaspoon salt, and 1/8 teaspoon pepper and cook, stirring, until heated through, about 2 minutes. Transfer to a serving dish and repeat with remaining ingredients.