Preheat your oven to 180°C (350°F). Grease and line a 9x12 inch cake tin.

In a pot, add the butter and dark chocolate. Heat over medium heat until melted and smooth, then leave aside to cool.

In a large bowl, whisk together the eggs and both sugars until lightened in color and almost doubled in volume.

Pour the cooled melted butter and chocolate into the egg mixture and whisk.

Add in the flour, cocoa powder, and salt. Whisk until you have a smooth batter.

Pour the batter into the prepared cake tin and bake for 35-40 minutes, or until a toothpick inserted into the center comes out with a few moist crumbs.

In a non-stick pot, add 1/4 of the sugar over medium heat. Stir until it starts to melt.

Add another 1/4 of the sugar and continue stirring until melted. Repeat this process until all the sugar is added and melted to a deep amber color.

Remove from heat and stir in half of the butter until smooth. Add the remaining butter and mix until smooth.

Slowly pour in the warm cream while mixing. Return to medium heat and cook for about 2 minutes to slightly thicken.

Remove from heat, mix in the salt and then the cornflakes.

Once the brownie has baked and cooled for about 10 minutes, spread the cornflake layer on top.

Refrigerate for at least 2 hours to set, preferably overnight. Once set, cut into slices and serve.