Preheat oven to 325 degrees F. Grease a 9 inch deep dish glass pie plate.
Melt the butter in a large saucepan or in a microwave-safe mixing bowl. Remove from heat, add the cocoa powder, and whisk until smooth. Whisk in the vanilla, then whisk in the sugar and the egg. Whisk in the baking powder and salt, and then gently stir in the flour.
Spread as evenly as you can in the pie dish and bake for 20 minutes or until top appears set, yet a little shiny. A toothpick inserted should come out with moist crumbs as opposed to batter. Set on a rack and let cool. Put in the freezer until ready to use or for at least an hour.
If desired, mix some of the Butterfinger into the softened ice cream. Another option is to just wait and put all the candy on at the end. Spread softened ice cream over top of brownie base. Drizzle caramel syrup over ice cream, and then spread a thin layer of whipped cream over the caramel syrup, dragging some of the syrup up into the whipped cream so that you have kind of a caramel-y whipped cream. Spread the remaining whipped cream over the top and pipe some around the edges (if you feel like it).
Sprinkle more Butterfinger candy over the whipped topping. Return to freezer for about 4 hours or until whipped cream is very firm.
When ready to serve, set the pie on a dish towel that’s been soaked in hot water. This will help loosen the crust from the side.. Cut slices and garnish with more caramel syrup and chocolate syrup (if desired).