Peanut-Toffee Shortbread

1 cup butter, softened
2/3 cup firmly packed light brown sugar
1/3 cup cornstarch
2 cups flour
¼ tsp salt
2 tsp vanilla
2 cups coarsely chopped honey-roasted peanuts, divided
1 (12-oz.) package semi-sweet chocolate chips

Beat butter at medium speed with an electric mixer until creamy.  Combine brown sugar and cornstarch; gradually add to butter, beating well.  Gradually add flour and salt to butter mixture, beating at low speed just until blended.  Add vanilla and 1 cup peanuts, beating at low speed just until blended.

Turn dough out onto a lightly greased baking sheet; pat or roll dough into an 11- x 14-inch rectangle, leaving at least a 1-inch border on all sides of baking sheets.
(A 10- x 15-inch jelly roll pan lined with parchment paper works well)

Bake at 350° for 20 minutes or until golden brown.  Remove baking sheet to a wire rack; sprinkle shortbread evenly with chocolate chips.  Let stand 5 minutes, gently spread melted chocolate chips over shortbread.  Sprinkle with remaining 1 cup peanuts, cool completely.  Cut or break shortbread into 2- to 3-inch irregular shaped pieces. 

(If using a jelly roll pan lined with parchment paper, carefully lift the entire cookie along with the parchment paper out of the pan.  Use a pizza cutter to cut into pieces.)