Preheat your oven to 350 degrees F.
In a medium saucepan or in the microwave, melt the butter. Take off the heat and stir in (by hand) the brown sugar, cocoa, eggs and salt until well combined. In a separate mixing bowl, mix the baking soda and flour together and then add slowly to the cocoa mixture. Stir (by hand) until well combined and then gently fold in the chocolate chips.
Refrigerate the dough for about 30 minutes.
When ready to bake, prepare your baking sheet with your non-stick baking mat or parchment paper. Take 1 heaped tablespoon of dough (or use your cookie scooper), use your finger to make a well or indentation in the center of the dough; fill the well with your dulce de leche and then top it up with more flattened cookie dough so you can seal the edges of the cookie.
Sprinkle with sea salt and bake for about 10 minutes.