Heat oven to 350°F (325°F for dark pan). Grease and flour 13x9-inch pan. In 1-quart microwavable bowl, place bittersweet chocolate, butter and 1 cup of the chocolate chips. Microwave uncovered on High 1 1/2 to 2 minutes, stirring twice, until melted and smooth. Cool slightly, about 5 minutes.
In large bowl, beat eggs, sugar and vanilla with electric mixer on medium speed until smooth. Add cooled chocolate mixture. Beat until well blended. Add flour, baking powder and salt. Beat on low speed until blended. By hand, stir in cookies and remaining chocolate chips. Pour into pan.
Bake 35 to 40 minutes or until edges begin to pull away from sides and center is set. Do not overbake. Immediately sprinkle candy on top of hot brownies. Let stand 10 minutes or until completely softened. Pull tip of toothpick through softened candy to spread and swirl. (It won’t completely cover top). Sprinkle with cashews. Cool until set, about 1 hour. For brownies, cut into 6 rows by 6 rows.