2. Add the mustard, lemon juice and vinegar and process until smooth.
3. With the processor running, add the olive oil slowly through the feed tube.
(This makes about 1/2 cup. Extra sauce can be stored in the refrigerator for up to 5 days and served with fish and shellfish.)
For the salmon burgers:
1. Cut the salmon into 1-inch pieces. Place the salmon in the food processor, fitted with the blade attachment. Coarsely grind the salmon.
2. In a small bowl, stir the egg, breadcrumbs, dill, shallots, capers, salt and pepper together. Add the ground salmon and stir to combine. Form the salmon mixture into 4 patties, about 1/2-inch thick.
3. Heat a nonstick skillet sprayed with nonstick spray over medium heat. Cook the burgers on both sides until the burgers are golden brown and just cooked through, about 3 minutes per side.
4. Meanwhile, toast the hamburger buns.
5. Serve the salmon burgers on the toasted buns with dill mustard sauce, lettuce and tomato.