Preheat oven to 375°F. In a large oven-safe pan over medium heat, add the butter and melt until it foams. Add the shallots, red wine, port, and thyme. Season with salt and swirl the pan to coat the shallots in butter and wine.
Cover and place in the oven for 20 minutes or until the shallots are tender and the wine has reduced to a glaze. (You may need to return the pan to the stovetop over medium-high heat for a few minutes, stirring continuously, to fully reduce the wine to a glaze consistency.) Discard the thyme and adjust seasoning with a touch of red wine vinegar and salt if necessary.