Preheat oven to 180°C/350°F (all oven types).

Butter and line a 20cm / 8" square tin with parchment / baking paper.

Place the ingredients in a small saucepan over medium high heat. Stir occasionally for the first 1 minute. When it is heated (ie. when you see wisps of steam), whisk constantly (leisurely, not vigorously!) for 7 minutes, ensuring the base doesn't catch (Note 3). It should be a pale golden colour.

Remove from stove and whisk for 30 seconds. Place lid on, set aside and keep warm.

Melt chocolate & butter: Place chocolate and butter in a bowl. Microwave in three 30 second bursts on high, stirring in between bursts, until melted and smooth.

Add sugar, eggs, vanilla: Add the sugar, eggs and vanilla extract to the chocolate mixture and mix well to combine.

Add dry ingredients: Sift in the flour, cocoa powder and salt. Mix until smooth and combined.

Reserve some batter: Measure out 1/2 cup of brownie batter and set aside. Pour the remaining batter into the prepared tin.

Pour over caramel: Pour the Salted Caramel over the brownie batter, getting as much coverage as you can (as you can't easily spread the caramel once poured). If caramel has cooled and is no longer pourable, reheat it on stove for 1 minute until runny again.

Cover with reserved brownie batter: Dollop the reserved 1/2 cup of brownie batter randomly over the Salted Caramel. Use a knife or skewer to make “swirls” - they won't be so visible once baked, it's more about spreading brownie batter over the caramel.

Bake: Place in the oven and bake for 30 minutes (for very gooey brownie, as pictured) to 35 minutes (for very moist but not super-gooey).

Cool: Leave to cool in pan for 10 minutes. Use surplus paper overhang to lift out onto a cooling rack. Cool for a further 20 minutes before slicing. Note: Caramel is a bit gooey when still warm but sets firmer once fully cooled, ie. it will cut through neatly.