Preheat oven to 350F degrees. Line baking sheets with parchment paper (do not use nonstick cooking spray).
In a large bowl, whisk together flour, baking powder, baking soda and salt, if using. Set aside.
Place the butter, shortening, and sugars in the bowl of a stand mixer fitted with the paddle attachment and beat on medium speed until creamy. Reduce the speed to low and add the eggs, one at a time. Do not overmix once the eggs are added. Add the vanilla. add the flour mixture a little at a time, and blend until smooth. Remove the bowl from the stand.
Mix by hand from this point forward.
Use a spatula or large spoon to fold in the oats, cornflakes, chocolate chips, nuts and dried cranberries.
Use a large cookie scoop or using a kitchen scale, measure 2.5 oz. balls, 3 tablespoons. Place round balls on the baking sheet, placing cookies about 2 inches apart.
Bake for 12-13 minutes, until cookies are barely golden on the edges, but still look a little underdone. Remove from the oven and cool for 5 minutes. Transfer to a wire rack to let cool completely.
Dough freezes well and cookies do too.