Preheat your oven to 350°F (175°C) and line a baking sheet with parchment paper.

Cream together the softened butter, granulated sugar, and brown sugar until light and fluffy.

Add in the eggs and vanilla extract, mixing until well combined.

Whisk together the flour, cocoa powder, baking soda, and salt in a separate bowl.

Fold the dry ingredients into the wet mixture until just combined, then fold in the chocolate chips if using.

Chill the dough in the refrigerator for at least 30 minutes.

Scoop about 1 tablespoon of dough, place Nutella and a half marshmallow in the center, and encase it with the dough.

Bake for 10-12 minutes until edges are set; the centers should be soft.

Allow cookies to cool for about 5 minutes on the baking sheet before transferring to a wire rack.