I found this recipe in a book on fine Scandinavian cuisine. It was delicious, and a definite keeper. Unfortunately, I used up all the pickled herring, and it was all eaten within minutes, so I'll need to wait until I do it again to take pictures. Here's the recipe though, in case you want to try it for yourself:

Pickled Herring Sushi-style

3/4 pound fingerling or Yukon Gold potatoes
1 tablespoon mustard oil or olive oil
1 teaspoon Dijon mustard
1 teaspoon rice vinegar
1/2 teaspoon wasabi powder
1/2 teaspoon kosher salt
4 whole pickled herring fillets or one 12-ounce jar (or two 6-ounce jars) pickled herring (home-style or in wine sauce,not in sour cream),drained
Purple Mustard (optional--as a garnish)

At Aquavit, we use a sushi mat to prepare these, but the potato mixture can also be simply shaped into logs on a cutting board, as described here.

1. Put the potatoes in a medium saucepan, add salted water to cover by 1 inch, and bring to a boil. Cook for 20 minutes, or until tender. Drain and let stand until cool enough to handle.

2. Peel the potatoes, put them in a medium bowl, and mash well with a fork. Add the mustard oil, Dijon mustard, rice vinegar, wasabi, and salt, and mix well.

3. Divide the potato mixture into quarters. On a board or other work surface, roll each portion under your palms into a log about 1 inch in diameter and 9 inches long.

4. If using whole herring fillets, slice them on the diagonal into 1/2-inch-wide strips. If necessary, cut any larger pieces of jarred herring in half, or trim them to fit the potatoes. Cut the mashed potato logs into 1-1/2-inch lengths. Stand them on end and top each one with a piece of herring. Serve at room temperature, or refrigerate and serve chilled.

5. Just before serving, garnish each piece of “sushi” with a dollop of purple mustard.

serves 6 to 8 as an appetizer, 8 to 10 as part of a buffet