In a small saucepan bring the port to a boil over high heat. Reduce the heat to medium and simmer for 12 to 15 minutes, until the port is slightly syrupy. You should have about 1/3 cup reduced port.

Place the port in a small bowl, stir in the vinegar, and let cool completely. Whisk the salt into the port until it is dissolved. Slowly whisk in the olive oil until emulsified. Season with pepper to taste.