Heat oven to 350°F. In small microwavable bowl, microwave butter and bittersweet chocolate uncovered on Medium (50%) 1 minute, stirring after 30 seconds. Microwave 30 seconds longer or until butter and chocolate are melted and can be stirred smooth. Set aside to cool slightly.
In medium bowl, stir together flour, granulated sugar, brown sugar and baking soda. Stir in egg, milk and cooled chocolate mixture until well blended.
In ungreased 8-inch square pan, press half of dough. Bake 8 minutes.
Meanwhile, in 1-quart saucepan, cook caramel topping and caramels over medium-low heat, stirring constantly, until caramels are melted.
Remove pan from oven. Carefully pour caramel mixture over partially baked base to within 1/2 inch of sides of pan. Sprinkle with cashews. Crumble remaining dough into small pieces and sprinkle over filling (some of filling will show). Bake 12 to 15 minutes longer or just until edges are set (do not overbake).
In small microwavable bowl, microwave chocolate candy bar pieces uncovered on High 30 seconds or until melted. Drizzle chocolate diagonally over baked bars. Cool completely, at least 1 hour. For bars, cut into 4 rows by 4 rows.