Preheat the oven to 400 degrees.
Slice the brussels sprouts in half and spread them out on a half sheet pan.
Grab a handful or two (personal preference) of grapes and toss them on.
Grab a handful or two or whole walnuts and add them too. (FYI - Martha does not roast the walnuts on the pan. She adds them in at the end. I personally think they taste better roasted.)
Drizzle enough olive oil on the above to just cover all of it.
Sprinkle the thyme over everything.
Roast for about 20 minutes, or until the brussels sprouts brown slightly.
If you can remember (which I usually don't), toss the mixture half way.
Remove from the oven and toss with 1-2 tbsp of balsamic vinegar.
Add salt and pepper to taste.
Serve warm.