Cook's Note: For a nonalcoholic version, substitute the port with 1/4 cup white grape juice mixed with 1/2 teaspoon vanilla extract.
In a medium bowl, combine the berries with 1 tablespoon port and 1 tablespoon sugar. Allow to sit and macerate while you prepare the zabaione.
Bring a small pot of water to a boil over medium heat. In a bowl that will fit over the top of the pot, beat the egg yolks with the remaining 1/4 cup sugar with an electric hand mixer until pale. Place the bowl over simmering water and, with the beater running slowly, drizzle in the remaining 3 tablespoons port. Continue to beat until the mixture becomes very thick and has doubled in volume, 5 to 10 minutes. Remove from the heat.
Divide half the berries among 4 serving glasses. Top each with a generous dollop of zabaione, garnish with the remaining berries and serve immediately.