Preheat the oven to 180C(fan)/350F/Gas Mark 4.
Prepare Brussels sprouts by trimming, peeling and washing them (See: How to prepare Brussels sprouts for roasting). Cut larger sprouts in half and leave small ones whole.
Put prepared Brussels sprouts in a large baking dish or tin, season with salt and pepper and drizzle with your choice of oil. Give them a good stir to ensure that they're nicely covered with oil.
Bake in preheated oven for 20-25 min until nice and brown (feel free to give them a stir halfway through roasting).
When Brussels sprouts are in the oven prepare the balsamic vinegar reduction by putting it in a small pan with maple syrup and bringing it to gentle simmer over low heat.
You want for the liquid to reduce nicely and become thick(ish) and sticky.
If adding walnuts, toast them first in a dry, non-stick pan until they start to brown ever so slightly. Make sure to keep an eye on them and shake the pan every few seconds to prevent them from burning.
Once Brussels sprouts are out of the oven, toss in toasted walnuts and drizzle over balsamic vinegar and maple syrup reduction.
Serve as is or add a handful of dried cranberries for a bit of sweet and sour vibe and some colour too.
Enjoy!