Preheat your oven to 425F and line one or two baking sheets with parchment. (The Brussels sprouts shouldn’t be crowded on the baking sheet, so if you have a smaller oven, use two sheets.)
Place the Brussels sprouts on the baking sheet(s). Whisk the melted butter, miso, and maple syrup together. The mixture will be thick and a bit sticky. Pour it over the sprouts, then use your hands to coat all of the Brussels sprouts with the miso butter.
Transfer the sprouts to the oven and roast them for 22-28 minutes, stirring once halfway through roasting. The sprouts should be tender and browning and have a glazed appearance. Enjoy!