Preheat the oven to 350ºF and line an 8-inch square baking dish with parchment paper.

In a medium saucepan over medium heat, melt the butter. Remove from the heat and stir in the cocoa powder until smooth and glossy. Whisk in both sugars. Add the eggs and vanilla, stirring until fully incorporated. Switch to a wooden spoon and stir in the flour, salt, and baking soda.

Pour batter into the prepared baking dish and bake for 25-28 minutes. Remove from the oven and allow to cool completely.

In the bowl of a stand mixer fitted with the paddle attachment, beat the cream cheese until smooth. Add the powdered sugar and continue beating until combined. Add half of the whipped topping, beating until incorporated.

Remove bowl from the mixer and fold in the rest of the whipped topping along with the chopped Butterfingers. Spread filling on top of cooled brownies, and place in the fridge while you make the ganache.

Place chocolate chips in a medium bowl; set aside. Pour heavy cream into a small saucepan and heat on the stove over medium-high heat. Once it starts to boil, immediately pour the hot cream over the chocolate chips. Cover with plastic wrap, and allow to sit for 5 minutes. Remove plastic wrap, and stir until smooth.

Allow ganache to cool for at least 15 minutes before pouring on top of Butterfinger Cream Filling layer. Either tilt the pan slightly to evenly cover everything, or use a knife to spread the ganache evenly. Refrigerate at least 2 hours to allow the layers to set up.

Just before serving, sprinkle the chopped Butterfinger bars on top. Slice into squares, and serve.