Shrimp Sandwiches with tarragon-caper mayonnaise

I made these shrimp sandwiches when I was home in California last month. They were a big hit and VERY easy to make. I subbed ciabatta bread instead of the buns, added a little extra hot pepper sauce to the mayo for more kick and BBQ the shrimp instead of cooking them in the pan. They say 'optional' for the avocado and tomato but I think those two things are a must.

Shrimp sandwiches with tarragon-caper mayonnaise
Bon Appétit August 2007
Makes 6 servings. Molly Stevens

1/3 cup mayonnaise
2 tablespoons drained capers, finely chopped
1 1/2 tablespoons grated sweet onion (such as Vidalia or Maui)
1 tablespoon chopped fresh tarragon
1/4 teaspoon celery seeds
1/4 teaspoon (or more) hot pepper sauce
1/2 cup finely chopped celery heart with leaves
2 tablespoons (1/4 stick) butter, room temperature
12 small (3-inch round) soft sandwich rolls or 6 hot dog buns, split horizontally1 pound cooked peeled deveined large shrimp, each cut horizontally in half
Tomato slices (optional)
Avocado slices (optional)
Thinly sliced butter lettuce (optional)

Mix first 5 ingredients and 1/4 teaspoon hot sauce in medium bowl. Mix in celery. Season with salt and pepper and more hot sauce, if desired. DO AHEAD Mayonnaise can be made 6 hours ahead. Cover; chill.Lightly butter cut sides of rolls. Heat griddle or large nonstick skillet over medium heat. Add rolls, buttered side down, to griddle and cook until golden, 1 to 2 minutes. Spread mayonnaise over bottom of each bun. Top with shrimp, tomato, avocado, and lettuce, if desired. Cover with top buns. Transfer to plates.

Shrimp Sandwiches with tarragon-caper mayonnaise