For ingredient substitutions, you can swap the brownie mix for a homemade brownie recipe. Feel free to use a different flavor of cookie dough or sandwich cookies (like chocolate chip) if desired. Optional variations include mixing in chocolate chips or nuts into the brownie batter or adding a drizzle of caramel sauce on top before baking. Store leftovers in an airtight container at room temperature for up to four days. To reheat, microwave a square for about 10-15 seconds.