View of Brace from the northern subsummit
Not sure if this is the shortest route, the southern trail may be shorter, but this one is really quick with 3 ups and 2 downs via the east and bags two other peaks on the way over. The trail to take is the Mt. Frissell Trail that ascends Round Mountain, then Mt. Frissell, and then on over to Brace Mountain. It's easy and fun with a little light scrambling early in the hike near the summit of Round Mountain.
Brace Mountain is a ridge of at least three distinct summits, the middle one being the higher. The Mt. Frissell Trail comes over from the east on Frisell, dips down to the state border, then ascends to the norther subsummit of Brace before turning left to the true summit. The summits are grassy and open with short bushes and plenty of small rocky openings to take a break on. Views are great on clear days north and south along the Taconics, east to Mount Frisell, Round Mountain, Bear Mountain and the Berkshires, and to the west are the Catskills. South is Riga Lake, a nice little gem tucked in the forest.
This hike is a nice way to enjoy western Mass, northwestern Connecticut and southeastern New York all in a few hours.
From there, continue on the trail and ascend up the east slopes of the northern subsummit of Brace and gain the ridge. From here you will come to this sign where you will turn left and follow the South Taconic Trail to the summit to the south (you will be able to see the large summit cairn with wind sock-see the Overview section photo above). I would recommend also continuing on south to the south summit (South Brace Mountain) to enjoy better views and places to hang out (plus it takes like 10 minutes to do so).
Return the same route. I am just guessing but I'd say this is about 2 miles one way from the trailhead with maybe 700 feet of elevation gain.