Preheat the oven to 180 degrees Celsius or gas mark 4.
In a pan on the hob, carefully melt the butter and the dark chocolate and mix together. Put to one side to cool.
Whisk together the eggs and the sugar until light and fluffy using an electric whisk or stand mixer. Pour the chocolate mixture into the whisked eggs and sugar and fold.
Add your flour and cocoa powder and fold again. Pour half of the mixture into a lined tin, then spoon the salted caramel milk chocolate spread on top.
Pour in the rest of the mixture and swirl the brownie with a skewer to bring the caramel to the surface.
Bake for 25-30 minutes, or until the middle no longer wobbles! Leave to set for a couple of hours, cut into squares and serve.