Line a rimmed baking sheet with foil. (Take care to avoid wrinkles.) Combine 2 cups melted chocolate and 1 1/2 cups nuts in a medium bowl. Scrape the mixture onto the foil and spread it into an approximate 12-by-9-inch rectangle. Sprinkle with additional finely chopped nuts, if desired. Refrigerate until set, about 20 minutes.

Transfer the bark and foil to a cutting board. Use a sharp knife to cut into 1 1/2-inch pieces.