I was first drawn to these cookies for the marbling effect created by folding and rolling together chocolate and peanut butter cookie doughs. The prep time is a bit long, but most of it is just chilling the dough to make it easier to work with. Shaping the dough would also be a fun activity to do with children.
Dutch processed cocoa powder has been treated with an alkalizing agent (potassium) to remove the acidity and bitterness associated with natural cocoa powder. This creates an enhanced cocoa flavor and a deeper reddish-brown coloring. Dutch processed cocoa powder is paired with baking powder in recipes, while natural cocoa powder is used with baking soda, an alkali. Natural cocoa powder is more common in the United States. In recipes, natural cocoa powder can be used as a substitute for Dutch process, but Dutch process can not be used as a substitute for natural. I have not been able to find Dutch processed cocoa powder in grocery stores in my area, but it is available on Amazon: Valrhona Chocolate Cocoa Powder and Rodelle Gourmet Baking Cocoa.
More information on Dutch processed cocoa powder.