Step 1

Arrange 2 racks to divide the oven into thirds and heat to 350°F. Using a large serrated knife, cut the bread at an angle into 1/2-inch slices. Arrange the slices on 2 large baking sheets, brush with the olive oil, and sprinkle with salt.

Step 2

Bake until the toasts are blonde and crisp, rotating the pans once or twice during baking, 10 to 15 minutes total. (Toward the end of baking, if the toasts aren't baking at the same rate, remove the browned ones so you can let the others continue baking.) Let the toasts cool on a cooling rack and serve within a few hours.

Step 3

Place the fish, butter, shallot, mustard, and cayenne in a bowl and beat with an electric hand mixer on high speed until the mixture is homogenous, scraping down the sides of the bowl with a spatula if needed, 1 to 2 minutes total. Taste and season with salt if needed; set aside. (Different fish have different saltiness levels, so it's important to taste before salting.)

Step 4

When ready to serve, stir the pickled vegetables and olive oil together in a small bowl. Spread about 1 tablespoon of the herring butter on each toast (you will have extra toasts; save for another use). Top each with a chubby pile of pickled vegetables and pinch of parsley.