For Shortbread:
- In large mixing bowl, cream butter, sugar, soy sauce and vanilla using an electric mixer on high speed.
- Sift flour and cocoa powder into butter mixture. Mix on low speed until just combined. Fold in chocolate chips using a stiff spatula.
- Place dough between two sheets of plastic wrap and press dough evenly into 8-inch square baking pan. Refrigerate 1 hour.
- Preheat oven to 325°F. and line baking sheet with parchment paper.
- Remove dough from plastic wrap; cut into 2-inch by 1-inch rectangles and place on prepared baking sheet. Bake for 20 minutes.
- Transfer parchment paper with cookies from baking sheet to wire rack. Cool cookies completely.
For Dipping Glaze:
- Heat white chips, heavy cream and soy sauce over a double boiler until half of chips are melted, stirring constantly. Remove from double boiler and continue to stir until mixture is smooth and all chips have melted.
- Let glaze cool for 5 minutes.
- Dip half of each cookie into glaze and place on baking sheet lined with parchment paper.
- Refrigerate cookies for 30 minutes, or until glaze is set.
