Weigh or measure all three sugars into a bowl and set aside. In another bowl, weigh or measure the flour, baking powder, baking soda, salt, and corn starch and set that bowl aside, run a whisk through to blend. In a stand or hand-held mixer, add the butter and all three sugars and mix on medium speed for 3 minutes. You want the butter and sugars well blended; the mixture should look lighter in color. I stop the mixer and scrape down the sides and across the bottom. Add the vanilla extract then the egg. Mix till incorporated.
Turn the mixer down to low and slowly add the flour mixture to the mixer bowl and incorporate. I stop the mixer and scrape down the sides and across the bottom to make sure all the flour is mixed into the wet sugar-butter mixture. I add the cranberries, bittersweet chocolate chip morsels, and chopped walnuts and turn the mixer on low to incorporate—about 30 seconds or less. I take the bowl off the stand and with a spatular turn the cookie dough over a few times to make sure everything is evenly mixed. Cover slightly and refrigerate for 30 minutes.
Preheat oven to 350°. Line 2 cookie sheet pans with parchment paper and set one aside. Using a medium scoop, add twelve scoops to a pan. Bake for 11-13 minutes and move to a cooling rack after you pull the baked cookies from the oven. This recipe makes about two dozen; I had enough cookie dough for two more cookies, so I rearranged my 12 scoops on the second round to accommodate the last two scoops of dough.