- 1/2 cup spicy brown mustard (such as Gulden's)
- 1/4 cup fresh lemon juice
- 2 teaspoons dry mustard
- 1/2 cup vegetable oil
- 4 tablespoons sugar, divided
- 3 tablespoons drained capers
- 1 1/2 tablespoons minced shallot
- 2 fennel bulbs, trimmed (fronds reserved), quartered, cored, thinly sliced crosswise (about 2 cups)
- 4 medium Persian or Japanese cucumbers, thinly sliced on diagonal (about 2 cups)
- Butter lettuce
- 1 pound assorted smoked fish (such as salmon, trout, whitefish, sturgeon, and black cod)
- Caper berries
- Lemon wedges
- Hard-boiled eggs, peeled, sliced (optional)
- Mix first 3 ingredients in 2-cup glass measuring cup; gradually whisk in oil. Season with pepper. Pour half of mixture into small bowl; mix in 3 tablespoons sugar, capers, and shallot for sauce. Mix 1 tablespoon sugar into remaining mixture. Reserve for dressing salad.
- Mix sliced fennel and cucumbers in large bowl. Mince enough fennel fronds to measure 3 tablespoons; add to bowl. Season to taste with dressing in measuring cup. Season with salt and pepper.
- Cover large platter with lettuce leaves. Arrange smoked fish and salad atop lettuce. Garnish with caper berries, lemon wedges, and eggs (if desired). Serve with bread, butter, and Mustard-Caper Sauce.