Preheat the oven to 400 degrees F.
In a large bowl, mix together the butter, miso, pepper and garlic. Add the Brussels sprouts, and toss; make sure to get all the sprouts coated with miso butter.
Spread the Brussels sprouts out on a baking sheet, cut side down. Roast until the sprouts are easily pierced with a knife and the outside leaves are crispy and brown, 25 minutes.
Sprinkle with sesame seeds. Serve immediately.