Step 1

Prepare the following, placing them all in a medium bowl: Thinly slice 1/4 medium fennel bulb (about 1 cup), 1 medium celery stalk (about 1/2 cup), and 2 medium radishes (about 1/4 cup). Finely chop 1 tablespoon preserved lemon rind. Juice 1/2 medium lemon, and add the lemon rind and 1 tablespoon of the juice to the vegetables. Toss to combine, taste, and season with more lemon juice and kosher salt as needed.

Step 2

Place 3 tablespoons mayonnaise and 1/2 to 1 teaspoon hot sauce in a small bowl and whisk to combine.

Step 3

Drain 1 can sardines. If desired, pick through the sardines and remove any bones. Spread the chile mayonnaise on both sides of 1 brioche bun. Pile the vegetable slaw on the bottom bun, then top with the sardines and a pinch of flaky salt if desired. Close the sandwich with the top bun.