1. Preheat oven to 350°. Bake pecans in a single layer in a shallow pan 8 to 10 minutes or until toasted and fragrant, stirring halfway through. Cool completely (about 15 minutes).
2. Beat butter at medium speed with an electric mixer until creamy. Stir together brown sugar and cornstarch; gradually add to butter, beating at low speed until well blended. Stir together flour and salt; gradually add flour mixture to butter mixture, beating at low speed just until blended. Add vanilla and 1 cup pecans, beating at low speed just until blended.
3. 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 sheet.
4. Bake at 350° for 20 minutes or until golden brown. Remove from baking sheet to a wire rack; sprinkle shortbread with chocolate morsels. Let stand 5 minutes; gently spread melted morsels over shortbread. Sprinkle with remaining 1 cup pecans, and let cool completely (about 1 hour). Cut or break shortbread into 2- to 3-inch pieces.