This dressing can be made the night before; assemble the salad just before serving.
In the bowl of a food processor, combine the olive oil, white-wine vinegar, 2 tablespoons dried cranberries, and sugar. Process until the dressing is pink and cranberries are very finely chopped. Season with salt and pepper.
Place the lettuce in a medium bowl, add the dressing, and toss to combine. Garnish with remaining dried cranberries, and serve immediately.