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.
Add the cocoa, salt and baking powder and stir until well combined.
Add the flour and stir until no floury patches are left.
Stir in the chocolate chips.
Set up a little bowl of water to dip your fingers in.
Using the 18/8 portion scoop, scoop 16 balls onto 2 sheet pans.
Lightly dampen your hand and roll each portion into a ball and place back on sheet pan.
Using a damp 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 dulce de leche.
Using the remaining dough, separate it into 16 pieces.
Gently flatten each piece enough to cover the top of the cookie, and press gently to seal the edges (you may need to dampen your finger if the dough has dried.
Sprinkle with fleur de sel or Maldon sea salt and bake for 10-12 minutes.