Using a handheld mixer, cream together the sugars and the butter until light in color and fluffy. It will be a bit chunky.
Add the eggs and vanilla and continue beating to incorporate.
Separately, sift together the AP flour. salt and baking soda.
Add the flour mixture to the wet ingredients and beat until just incorporated.
Stir in the cocoa. Stirring it in will give you a marbled effect.
Stir in your chocolate chunks.
Bake in a preheated oven at 170FAN/350F for 13-15 minutes (mine always take exactly 13:30!) and then cool the cookies on a wire rack. Store in an airtight container.