Bring a large saucepan of generously salted water to a rolling boil. Add the green beans and cook until al dente, 6 to 8 minutes. Drain thoroughly and set aside.
Return the saucepan to medium heat. Melt the butter, then add the garlic and sauté until softened, about 30 seconds. Whisk in the brown sugar, sherry, and cider vinegar. Add the green beans and toss until well coated.
Add the almonds, 1/2 teaspoon salt, and the pepper and toss until well combined. Remove from the heat. Transfer to a serving dish. Serve hot.
Store leftovers in a covered container in the refrigerator for up to 3 days.