In a small bowl, stir together the sherry, soy sauce and chili paste; set aside.
Trim the stem ends from the bok choy and separate into leaves. In a wok or large nonstick fry pan over high heat, warm 1/2 Tbs. of the oil. When the oil is hot, add the bok choy and cook, stirring, until just crisp-tender, about 2 minutes. Transfer to a bowl.
Warm the remaining 1/2 Tbs. oil in the wok. When the oil is hot, add the garlic and ginger and cook, stirring, until fragrant but not browned, 15 to 30 seconds. Add the beef and cook, stirring, until no longer pink, about 2 minutes.
Return the bok choy to the wok along with the sherry mixture and cook until heated through, about 1 minute. Serve immediately. Serves 4.