You will also need a 20cm (8 inch) square baking tin, greased and lined with baking parchment
Preheat the oven to 170ºC/325ºF/gas mark 3.
Combine the dark and 25g of milk chocolate in a heatproof bowl. Add the butter and melt together carefully in a microwave in 20 second bursts or over a pan of simmering water. Stir until smooth and combined and leave to cool slightly.
Add the sugar, vanilla and beaten eggs to the melted chocolate and butter and mix to combine.
Sift both of the flours and cocoa powder into the bowl and mix until smooth. spoon into the prepared tin. Spread level with a palette knife and bake on the middle shelf of the preheated oven for *25 minutes.
*For a clean cut wipe the knife with a damp cloth between cuts
Leave to cool in the tin, heat the chocolate spread slightly in the microwave. Spread in an even layer over the cooled brownies, sprinkle with the sprinkles then cut into squares, chill in the fridge for at least an hour then devour.