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

Cream the softened unsalted butter, light brown sugar, and granulated sugar in a large mixing bowl until the mixture is light and fluffy, about 2-3 minutes.

Beat in the large egg and egg yolk until fully combined, ensuring the batter is smooth and creamy.

Stir in the 2 teaspoons of vanilla extract.

Gradually add the 1.5 cups of all-purpose flour and 2/3 cup of unsweetened cocoa powder, stirring just until combined.

Fold in the mini semi-sweet chocolate chips, large marshmallows, graham cracker chunks, and dark chocolate bar pieces.

Scoop the cookie dough onto the prepared baking sheets, placing them about 2 inches apart.

Bake in the preheated oven for 11 minutes, or until the edges are set and the centers are still a bit soft.

Allow cookies to cool on the baking sheets for a few minutes before transferring to a wire rack to cool completely.

Optional: Sprinkle a pinch of sea salt on top before serving.