To make the cookie dough crust: Preheat oven to 350° F. In a large bowl, cream together butter, sugars, eggs and vanilla. In a separate bowl, mix flour, cocoa powder, salt, and baking powder. Add flour mixture to butter mixture and mix until thoroughly blended. Stir in semi-sweet chocolate chips, marshmallows and chopped pecans. Pat cookie dough into greased pizza pan. Bake for approximately 20 minutes until lightly browned around the edges. Remove from oven and while still warm, scatter the marshmallows over the cookie base pizza. Then scatter the chocolate chips and drizzle with caramel topping. Scatter the nuts over the top. Return to the oven and bake for approximately 10 more minutes or just until the marshmallows start to melt but are not browned. Cool completely and then cut into wedges with a dollop of whipped cream and a stemmed maraschino cherry on top of each slice.