Scallop and Apple Tartare

Name: Scallop and Apple Tartare
Ingredients: 8 ounces fresh sea scallops (preferably diver scallops); 1/3 cup finely chopped unpeeled Granny Smith apple (from 1 medium [8-ounce] apple); 1 large (2-ounce) shallot , very thinly sliced lengthwise; 1 medium celery stalk , finely chopped (about 1/4 cup); 1/4 cup celery leaves (from 4 celery stalks); 3 tablespoons fresh lemon juice (from 1 lemon); 3 tablespoons extra-virgin olive oil; Kosher salt, to taste; Toasts, crackers, or endive spears, for serving