In a saucepan, melt 3 tablespoons of the butter. Add the onion and cook over moderate heat until softened, 7 minutes. Add the red wine, beef stock and thyme and bring to a boil. Simmer until the liquid has reduced to 3/4 cup, 1 hour and 15 minutes; strain into a clean saucepan. Season with salt and pepper, cover and keep hot.