Brussels Sprouts in Brown Butter

2 pints Brussels sprouts
2 tablespoons unsalted butter
1 tablespoon sherry vinegar, or balsamic or red-wine vinegar Salt and freshly ground black pepper to taste

Trim the Brussels sprouts and cut an X into the base of each.
Steam the Brussels sprouts for 10 minutes. Remove from heat.
Melt butter in a large skillet and cook until it turns nut-brown in color.
Just before serving reheat butter, add Brussels sprouts and toss until well coated and warmed. Add vinegar, season to taste and serve.