In a small skillet, bring the port to a boil. Cook until reduced to about 1 tablespoon, 3 to 5 minutes. Set aside.
In a small saucepan, combine the milk and cream; bring to a simmer. Whisk in the chocolate until combined; transfer to a blender with the foie gras. Blend the foie gras hot chocolate until smooth.
Pour the hot chocolate mixture into serving cups; drizzle each with the reduced port and sprinkle with sea salt. Top with marshmallows and, if desired, use a torch to lightly brown.
This recipe was provided by professional chefs and has been scaled down from a bulk recipe provided by a restaurant. The Food Network Kitchens chefs have not tested this recipe, in the proportions indicated, and therefore, we cannot make any representation as to the results.