Preheat your oven to 180°C (350°F) and line a square baking dish (about 8x8 inches) with parchment paper.

In a mixing bowl, combine the melted butter and granulated sugar. Stir until well combined.

Add the eggs and vanilla extract to the butter-sugar mixture. Mix until the batter is smooth and creamy.

In a separate bowl, sift together the flour, cocoa powder, baking powder, and salt. Gradually add this dry mixture to the wet ingredients, stirring until a thick brownie batter forms.

Spread the brownie batter evenly into the prepared baking dish.

Place the Oreo cookies on top of the brownie batter in a single layer.

Now, let's make the chocolate chip cookie layer.

In a separate bowl, cream together the softened butter, light brown sugar, and granulated sugar until light and fluffy.

Add the egg and vanilla extract to the butter-sugar mixture. Mix well.

In another bowl, sift together the flour and baking soda. Gradually add this dry mixture to the cookie dough, mixing until everything is well combined.

Fold in the chocolate chips.

Drop spoonful of the chocolate chip cookie dough over the brownie layer and Oreo cookies, spreading them out evenly.

Bake in the preheated oven for 25-30 minutes or until the Brookies are set but still slightly gooey in the centre.

Allow the Oreo Brookies to cool in the baking dish for about 15 minutes, then transfer them to a wire rack to cool completely.

Once cooled, cut into squares and enjoy your delicious Oreo Brookies!