Slice the onion into quarters and slice into thin eyebrow shapes.
In a medium frying pan melt the butter and saute the onions over medium heat for about 10 minutes or until tender.
Add the thyme and white wine and continue cooking until golden brown, about 20-30 minutes total.
While the onions are cooking preheat the oven to 355. Line a small baking dish with parchment paper and cut the rind off of one of the flat sides of the brie.
Place the brie cut side up into the lined dish. Cover the brie with all of the cooked onions and bake for 30-40 minutes or until the cheese is melted and bubbly. Serve with a baguette and enjoy!