Preheat your oven to 180°C (350°F). Grease and line a 9x12 inch cake tin with parchment paper to ensure your brownies come out easily after baking.

In a pot over medium heat, combine the unsalted butter and dark chocolate. Stir gently until both have melted and the mixture is smooth. Alternatively, you can melt them together in the microwave in short bursts, stirring between each. Set aside and allow to cool.

In a large bowl, add the eggs, packed brown sugar, and granulated sugar. Whip the mixture with an electric mixer or a whisk until it lightens in color and nearly doubles in volume. Carefully pour in the cooled melted butter and chocolate from Step 2, whisking to combine. Sift in the all-purpose flour, unsweetened cocoa powder, and salt. Whisk gently until a smooth batter forms, taking care not to overmix.

Pour the brownie batter from Step 3 into your prepared cake tin. Smooth the top evenly. Bake in your preheated oven for 35–40 minutes, or until a toothpick inserted into the center comes out with a few moist crumbs. Once done, remove from the oven and allow to cool for about 10 minutes.

In a non-stick pot with high sides, add about a quarter of the granulated sugar and place over medium heat. As the sugar melts, gradually add the rest of the sugar in quarters, stirring constantly to ensure even melting. Continue heating and stirring until all sugar is melted and turns a deep amber color. Immediately remove from heat and add half of the room temperature unsalted butter, stirring until combined, then add the remaining butter. Slowly pour in the warmed heavy cream while stirring. Return the pot to medium heat and cook for 2 minutes to thicken slightly. Remove from heat, then stir in the salt and cornflakes until everything is evenly combined. I like to taste the caramel at this stage and adjust the salt to my liking for a perfect balance of sweet and salty.

Once the brownies from Step 4 have cooled for about 10 minutes, spread the cornflake caramel layer from Step 5 evenly over the top. Smooth the surface with a spatula. Place the tin in the fridge and leave to set for at least 2 hours (though I prefer to leave it overnight for the best texture and flavor).

When the brownies are fully set, remove them from the tin, slice into squares, and enjoy with friends and family. These are perfect with a cup of coffee or as a decadent dessert.