Preheat oven to 175C. Grease an 8" X 8" pan. Line with parchment paper. Grease it.
In a saucepan, combine chocolate, 4 tablespoons butter, and 1/4 teaspoon salt. Melt on medium-low heat for 4 minutes or until smooth. Remove from heat. Stir in 3/4 cup of sugar and vanilla extract. Stir in the eggs, one at a time, until well blended.
Into the same pan, sift cornflour and cocoa. Fold in to incorporate. Stir batter rigorously for at least 1 minute or until it thickens slightly and begins to pull away from the sides of the pan. Fold in 1 cup chopped nuts.
Spread evenly into the baking pan. Bake for 25-27 minutes or till a toothpick inserted in thecentercomes out clean. Cool on a wire rack.
Meanwhile, take a saucepan and put the remaining 3/4 cup of sugar into it along with corn syrup and 1/4 teaspoon salt. Cook on medium-high heat for 9 -12 minutes, till the mixture turns amber in colour. Swirl the pan to get an even colour.
Working quickly, remove the pan from heat and add the cream. Once the bubbling subsides, add the remaining 2 tablespoons butter until well incorporated. Stir in the remaining chopped nuts. Pour the mixture over the cooled brownie, tilting the pan to spread evenly. Let it stand for at least 2 hours or till it sets.
Cut into desired sizes. Store them in an airtight container, layered with waxed paper, at room temperature, for up to 2 days.