Brownie Layer: Line a 8x8-inch baking pan with overhanging parchment paper. Prepare and bake brownies according to package directions. Let cool completely. You can refrigerate or freeze to speed cooling process.
Cookie Layer: In a large bowl, add Walnut Chocolate Chip Cookie Mix, 1/2 cup butter and 1 tablespoon milk. Stir until well combined.
Remove 1/4 cup toffee bits from package and reserve for topping. Add remaining toffee bits to cookie dough batter and stir until completely combined. Press cookie dough firmly and evenly over cooled brownies.
Chocolate Ganache: Add heavy cream and butter to a large microwave safe bowl and heat for one minute, stir to combine. Heat at 30 second intervals if butter is not completely melted at this point. Add chopped chocolate and stir until chocolate is melted. Pour Chocolate Ganache over brownies and spread evenly.
Top with reserved 1/4 cup Toffee Bits and 1/4 cup mini chocolate chips.
Refrigerate Cookie Dough Brownies for at least 2 hours before cutting. Store in the refrigerator.