Preheat oven to 350 degrees F (175 degrees C). Grease and flour a 9x13 inch baking pan.
In a large bowl, cream together the butter and 1 cup of sugar until light and fluffy. Beat in the eggs, one at a time, then stir in the vanilla. Combine the flour, baking soda, baking powder and salt; stir into the creamed mixture alternately with the milk. Spread half the batter into the prepared pan.
In a small bowl, mix together the cocoa powder, chocolate chips, walnuts, 1/2 cup sugar and 1/2 cup flour. Cut in the 1/4 cup of butter until the mixture is crumbly. Sprinkle the cocoa mixture over the batter in the pan.
Spread the remaining batter evenly over the cocoa layer and sprinkle with the remaining crumb mixture. Bake for 35 to 40 minutes in the preheated oven, or until a toothpick inserted into the center of the cake comes out clean.
Cool the cake in the pan for at least 10 minutes before serving.
Interesting Facts
This cake can be stored in an airtight container in the refrigerator for up to 1 week.
This cake can also be frozen for up to 3 months.
Cocoa powder adds a rich chocolate flavor to the cake.
Chocolate chips and walnuts add a delicious crunch to the cake.