Preheat oven to 350°.While the oven is preheating make the cookie dough.
Cream together the butter and sugar until light and fluffy.
Scrape the sides, add in the eggs, vanilla and peanut butter. Beat until mixed.
Scrape the sides and add in the flour, baking powder and cornstarch. Mix until thoroughly combined.
Use a scoop to create equal sized cookies. Double scoop the cookie dough to make large bakery style cookies (more details given above).
Flatten the cookie dough by gently pressing the bottom of a drinking glass down on the center of the cookie dough. Repeat with remaining dough. The cookies will spread slightly so make sure to leave room. I tend to only put 6 cookies per pan.
Bake at 350° for 9-11 minutes or until the centers of the cookies have puffed up and are no longer glossy.Cool Completely.
Microwave the heavy cream until boiling (about 2 minutes) and then pour the chocolate chips into the hot cream.
Let the chocolate chips and hot cream sit for 5 mintues. After teh 5 minutes is over, stir until smooth.
Let the Ganache cool and thicken slightly and then spoon and spread ganache onto each cookie.
Refridgerate the cookies until ready to serve. About 20 or 30 minutes before serving, remove from the fridge and sprinkle with powdered sugar.