Melt the butter in a saucepan over low heat.

Once the butter is melted, remove the saucepan from the heat and add finely crushed chocolate. Mix well until smooth.

In a large bowl, beat the eggs. Gradually add the brown sugar in two parts, beating until the mixture triples in volume.

Add the melted chocolate from step 2 to the beaten eggs and mix quickly.

Add the whole wheat flour, baking powder, cocoa powder, crushed walnuts, and salt. Mix quickly and roughly.

Line a 8x8 inch square baking pan with parchment paper (with the sides up) and pour in the batter.

Arrange the roughly crushed Oreo cookies on top of the batter.