01 - Preheat oven to 425°F and line a baking sheet with parchment paper.
02 - In a large mixing bowl, combine maple syrup, olive oil, balsamic vinegar, sea salt, and black pepper. Whisk until fully blended.
03 - Add trimmed and halved Brussels sprouts to the bowl and toss well to ensure even coating.
04 - Spread the Brussels sprouts, cut-side down, in a single layer on the prepared baking sheet.
05 - Roast for 15 minutes, then remove from the oven.
06 - Sprinkle the chopped walnuts over the Brussels sprouts and toss gently. Return pan to oven and roast for an additional 8 to 10 minutes, until sprouts are golden and walnuts are toasted.
07 - Transfer the roasted Brussels sprouts and walnuts to a serving bowl. Garnish with chopped parsley if desired, and serve warm.