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.
1. Chocolate - You must use baking chocolate which you will find in the baking aisle at supermarkets. Not regular dark chocolate made for eating! (Well, you can eat the baking chocolate if you want ;) )2. Golden syrup is like a cross between honey and molasses – it is thick and sweet but not as thick as molasses. It is mainly used for colour in this recipe so you can substitute with maple syrup, or even leave it out.3. Caramel - The condensed milk has a tendency to catch on the bottom of the saucepan which will result in golden bits distributed throughout. Don’t despair if this happens, you will barely notice it once baked. But you do need to whisk consistently to ensure you don’t end up with a sticky, burnt mess in the saucepan!4. Baking time - The bake time is slightly longer than when you are making a plain brownie because of the caramel layer, which causes the brownie to take longer. 5. Measures - Tablespoon and cup measures differ from country to country. For this recipe, the difference is not enough to impact it. I have made it with both US and Australian measures (the two countries at the extremes in difference) and could not tell the difference. The only exception is Japan – please use weight measures provided (your cups are far too small).6. Nutrition per brownie, assuming you cut it into 16 squares as directed, rather than into 4 very large squares (tempting as that might be).