Preheat oven to 325°F. In large bowl, beat butter and sugar until light and airy (about 3 minutes). Beat in vanilla.
In separate bowl, combine flour, cornstarch and salt; add into butter mixture and mix until just combined. Fold in roughly chopped chocolate.
Drop by 1 tablespoon, onto parchment-lined baking sheets making sure each round is 2 inches apart. Flatten slightly, pressing 1 slice of Toblerone onto each round. Refrigerate until firm (about 15 minutes).
Bake for 15 to 18 minutes, until edges are golden. Let cool for 5 minutes until transferring to a cooling rack. Cool for 15 minutes before enjoying!