Preheat your oven to 350°F (175°C) and line your baking sheets with parchment paper. This ensures an easy release once the cookies are baked to perfection.

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

Add in the egg and egg yolk, mixing well until completely incorporated. This will enhance the richness in your cookie dough.

Stir in the vanilla extract, allowing the sweet aroma to fill your kitchen. This step adds that delightful warmth to your dough.

Gradually mix in the all-purpose flour and cocoa powder until you see no dry flour remaining. Be careful not to overmix; your cookies will thank you!

Fold in the mini semi-sweet chocolate chips, marshmallows, graham cracker pieces, and dark chocolate bar pieces gently. The goal is to have an even distribution of these delicious mix-ins.

Scoop generous portions of cookie dough onto the prepared baking sheets, making sure to leave space between each scoop for spreading.

Bake the cookies in the preheated oven for 11 minutes, or until the edges appear set but the centers are still slightly soft—this ensures that gooey texture!

Cool the cookies on the baking sheets for a few minutes before transferring them to a wire rack. This helps them firm up slightly while retaining that melty goodness.

Optional: Drizzle with melted chocolate for an extra touch of indulgence!