Brownie:

• Pre-heat the oven to 175°C (350ºF) and grease a large spring-form pan (mine was 26cm / 10¼".
• Slowly heat the chocolate and butter in a pan until just melted.
• Add the coffee (or milk, if that's what you are using) and give the mixture a quick stir.
• Set to one side while you prepare the next step.
• In a large bowl, whisk the sugars and eggs together, followed by the vanilla.
• Finally, pour in the cooled chocolate mixture. Stir until combined.
• Combine the flour and cocoa (you can sift it, if you like), and stir into the wet ingredients, mixing until just combined.
• Pour into the prepared tin and bake for around 20 minutes. The brownie is ready when the top is spongey but firm to the touch. Set to one side to cool for a while (leave the cake in the pan).
• Stir the cashews into the dulce de leche and spread evenly over the top of the brownie. 
• Melt the milk chocolate in a Bain Marie (double boiler), or carefully in the microwave.
• When melted, pour over the caramel, spreading it with a knife to achieve an even coverage.
• Place the cake in the fridge for at least four hours (preferably overnight) to set (see note 3).
• When ready to eat, cut the cake into slices. Because the topping is just milk chocolate, it will set really hard. Therefore, it's possible it might crack (mine did). To try to prevent this from happening, use a sharp knife that has been run under the hot tap.