Preheat oven to 400 degrees Fahrenheit.
Trim ends on brussel sprouts then cut in half.
On a baking sheet, toss brussels with 2 tbsp olive oil and salt. Spread out in a single layer and roast in oven for 15-20 minutes.
In the meantime, in a large bowl, mix miso paste, vinegar, and 1 tbsp olive oil until evenly combined.
Once brussels have roasted toss in bowl with miso mix. Mix until everything is evenly coated. Spread back out on baking sheet in a single layer and bake for an additional 5 minutes.
Remove from oven, and top with balsamic reduction before serving.