Heat the butter in a pan. Cover the onions and sauté for approx. 15 mins., stirring occasionally. Pour in the wine and reduce almost completely. Add the water and all the other ingredients up to and including the pepper, simmer over a medium heat for approx. 20 mins., stirring occasionally, allow to cool slightly.
Mix the butter with the thyme and salt. Spread the mixture onto the sliced bread, toast in a frying pan for approx. 2 mins. on each side, remove.
Top the warm crostini with Brie, onion confit and pork.