Pre-heat the oven to 120C.Line a baking sheet with baking paper. Place the flour on top and bake for 30 minutes. Allow to cool.
Add the butter, sugar and vanilla into a large mixing bowl. Use an electric mixer to whip together until well combined, creamy and pale in colour.
Add the warm milk and mix until well combined. Add the flour and mix until well combined. Lastly, add the white chocolate chips, rainbow sprinkles and chocolate sprinkles and mix until well combined.
Line an 8” (4-inch tall) cake tin with plastic wrap. It might even be easier to line it with a plastic shopping bag.
Place the first layer of brownie in the bottom. Top with half the cookie dough. Use clean hands or the back of a tablespoon to press the cookie dough down firmly. Place the second brownie layer, followed by the second half of the cookie dough. Then place the final brownie layer on top. Place in the fridge for 2 hours.
To take the cake out of the tin, turn it upside down and slowly wiggle it out of the tin. If it feels stuck in there, shake the cake up and down to encourage it to make its way out. Make sure you’re doing it over a table, so it doesn’t pop out onto the floor.
Place the cake onto a serving dish and drizzle the chocolate sauce on top.
Add the whipped ganache in a large microwave safe bag fitted with an open star tip. Pipe swirls of frosting on top of the cake. Finish with a generous sprinkle of rainbow sprinkles.
Cake can be stored in an airtight container in the fridge for up to three days.