You can use any fancy caramel on this cookie--my friend Christine's Little Flower Caramels are great, but super-market Lancaster or Werther's soft caramels are good option.
1 1/2 cups unbleached all purpose flour
1/3 cup powdered sugar
1 tablespoon cornstarch
1/2 teaspoon salt
10 tablespoons (1 1/4 sticks) unsalted butter, cut into 10 pieces, cool room temperature
1/2 cup finely chopped toasted walnuts
12 (about) soft caramels, cut in half
4 ounces bittersweet or semisweet chocolate, melted
1 cup coarsely chopped toasted walnuts
Sea Salt for sprinkling (optional)
1. Using an electric mixer, mix the flour, powdered sugar, cornstarch and salt in a large bowl to blend. Add the butter and mix on low speed until dough forms. Roll the dough into an even 10-inch log. Wrap the log in waxed paper and refrigerate until firm, about 2 hours. (Can be prepared up to 4 days ahead.)
2. Preheat the oven to 350°F. Line 2 heavy large baking sheets with parchment. Using a long sharp knife, slice the dough into thin rounds. Arrange the rounds on prepared baking sheets, spacing evenly.
Bake until golden brown, about 10 minutes.
3. Place a piece of caramel atop half of the cookies. Return the cookies with the caramels to the oven and continue baking until caramel spreads to about a 1-inch round, about 2 minutes. Remove the cookies from the oven. Place a plain cookie atop cookies with caramel, forming a sandwich. Cool completely.
4. Drizzle chocolate over the cookies and sprinkle with the coarsely chopped nuts. Sprinkle lightly with salt if desired. Chill until chocolate sets. Store the cookies in an airtight tin up to 3 days.