In a small bowl, stir together the hand vinegar.

Lay a sushi mat on a clean surface and cover with plastic wrap. Place a sheet of nori on the mat, shiny side down. Moisten hands with hand vinegar and shake off excess. Spread half the rice across the nori. Sprinkle the rice with 1 teaspoon caraway seeds. Turn the nori over so that the rice side is down.

Cover half the rice, crosswise, with 3 slices corned beef. Spread the corned beef with 2 teaspoons horseradish. Cover the corned beef with half the cheese.

Securing the meat and cheese with your fingers, use your thumbs to push the end of the mat up and over the filling, until the edge of the nori meets the rice on the other side. Press firmly on the roll.

Lift up the top of the mat and roll firmly until tight and round. Squeeze gently to shape the roll. Press the ends in carefully to secure any loose rice. Remove the bamboo mat and set the roll aside.

Make the second roll in the same manner.

Use a very thin, sharp knife to cut each roll into 8 slices. Arrange on a sushi platter and serve with Dijon mustard.