Combine the crème fraîche, mustard, dill, and salt. Cover and refrigerate up to 1 day ahead.
Arrange the bread slices on baking sheets. Toast until lightly browned; turn and toast the other sides.
Remove from oven and rub 1 side of the toasts with a cut shallot. Cut each slice into 4 triangles. Serve with the salmon, sauce, toasts, and lemon slices.