I spotted this on twitter today and thought I'd make it for next time I do salmon.
Ingredients-:
½ small shallot, chopped
2 cornichons, chopped
1 garlic clove, chopped
¾ cup mayonnaise
2 Tbsp. finely grated fresh horseradish or 1 Tbsp. drained prepared horseradish
1 Tbsp. chopped fresh flat-leaf parsley
2 tsp. drained capers
2 tsp. whole grain mustard
1 celery stalk, chopped
2 tsp. finely grated lemon zest
1 Tbsp. fresh lemon juice
¼ tsp. cayenne pepper
Kosher salt and freshly ground black pepper
Preparation-:
Purée celery, shallot, cornichons, garlic, mayonnaise, horseradish, parsley, capers, mustard, lemon zest, lemon juice, and cayenne in a blender or food processor until smooth; season with salt and pepper.
http://www.bonappetit.com/recipe/comeback-sauce?mbid=social_twitter
DO AHEAD: Sauce can be made 2 days ahead. Cover and chill.