Preheat your oven to 350°F (175°C). In a large mixing bowl, combine the flour, cocoa powder, sugar, baking powder, and salt. Add eggs, melted butter, and vanilla extract, and stir until the batter is smooth. Pour into a greased 8x8-inch baking pan and bake for 20-25 minutes, or until a toothpick inserted comes out clean. Allow brownies to cool.

In a saucepan, melt butter over medium heat. Add heavy cream and brown sugar, stirring constantly until the mixture thickens and becomes smooth, about 5-7 minutes. Stir in vanilla extract and remove from heat.

Cut the cooled brownies into squares. Place one square on each serving dish, then top with a generous scoop of vanilla ice cream. Drizzle with warm caramel and chocolate sauce.

Add a dollop of whipped cream on top, then sprinkle with chopped nuts (if using). Garnish with a maraschino cherry for a perfect finish.

Serve immediately and enjoy your indulgent homemade Thunder from Down Under!