Lightly grease a 9x9-inch baking pan and line it with parchment paper for easy removal. In a mixing bowl, cream together the butter and brown sugar until the mixture is light and fluffy. Add the egg and vanilla extract, and beat until well combined. In a separate bowl, sift together the flour, baking powder, and baking soda. Gradually add the dry ingredients to the creamed mixture, folding gently until fully incorporated. Stir in the chocolate chips. Spread the dough evenly into the prepared baking pan and bake at 350°F (or 325°F if using a glass dish) for 15 minutes. Once out of the oven, immediately sprinkle the surface with broken Oreo pieces and caramel candies. Then, pour the brownie batter evenly over the top, ensuring everything is covered.

In a small bowl, sift together the flour, cocoa powder, and salt, then set aside. In a saucepan over low heat, melt the butter and unsweetened chocolate together, stirring until smooth. Remove from heat and allow the mixture to cool slightly until lukewarm. Add the eggs, vanilla extract, granulated sugar, and brown sugar to the chocolate mixture, stirring thoroughly until the sugars have dissolved. Gradually add the sifted dry ingredients and stir until the batter is smooth and well blended. Pour the brownie batter over the Oreo and caramel layer in the pan. Return the pan to the oven and bake for an additional 15 to 20 minutes, or until the surface of the brownie layer is set and no longer glossy. Allow the dessert to cool completely before topping with ganache or cutting into squares.

Heat the whipping cream until just below boiling point—you can do this quickly in the microwave. Pour the hot cream over the chocolate chips and let it sit for about 5 minutes. Then, stir the mixture until smooth and glossy. Transfer the ganache to a Ziploc bag, snip off a small corner with scissors, and drizzle it over the cooled squares in a thin, continuous circular pattern. Cut into 2-inch squares and serve.