Preheat the oven to 410°F. Line two large baking sheets with parchment paper.
Beat cold cubed butter with both sugars in a stand mixer using the paddle attachment for about 2 minutes, until combined but still chunky.
Add eggs and vanilla. Mix just until incorporated.
Whisk together flour, cornstarch, baking soda, baking powder, pumpkin pie spice, cinnamon, and salt in a separate bowl.
Add the dry mixture to the wet ingredients on low speed until a thick dough forms.
Fold in the Pumpkin Pie M&M’s and white chocolate chunks.
Portion dough into 5–6 oz mounds (about ¾ cup each). Keep tall, rough shapes- do not flatten.
Bake 9-11 minutes, until the tops are golden and just set but the centers still look soft.
Cool cookies on the pan for 30 minutes before transferring to a cooling rack; they’ll finish setting as they rest. Let them sit for a few hours before serving.