Line a baking tray with parchment paper. Preheat your oven to 350 degrees F (180 degrees C)
In a medium saucepan, melt the butter. Take off the heat and stir in the brown sugar and eggs. Then add the cocoa, salt and baking powder and stir until well combined. Add the flour and stir until no floury patches are left. Lastly stir in the chocolate chips.
Make the caramel, if using (see notes for recipe)
Take 1 heaped tbsp of dough, use your finger make a large indentation the centre of the dough; fill the indentation with a small blob of nutella (like 1/2 tsp ish), and top it up with the still-warm salted caramel, or a caramel-filled chocolate. Top with a flattened tablespoon of dough, and seal the edges. (see .gifs below recipe)
Sprinkle with fleur de sel and bake for 8-10 minutes.