Prepare two baking sheets. Line each cookie sheet with parchment paper and set aside.
In a mixing bowl, whisk together all dry ingredients including flour, cinnamon, salt, baking soda, and cornstarch. Set aside.
In the bowl of a stand mixer with the paddle attachment (or in a mixing bowl with a hand mixer), beat the butter and both sugars together until well creamed. Add the mashed overripe bananas and mix.
Add the egg and vanilla extract, mixing just until everything is combined.
Add the dry ingredients into the wet ingredients, mixing only until just incorporated. Be careful not to overmix.
Mix in the chopped white chocolate and broken graham crackers by hand.
Using a large cookie scoop, portion up to 8 heaping scoops (approximately 3-3.2 oz) of dough onto each prepared baking sheet, spacing them evenly apart.
Refrigerate the scooped cookie dough on the baking sheets for 60 minutes if you used cold butter and 2 hours if you used room temperature, softened butter. *(see note)
Preheat oven to 350℉.
Bake for 18-22 minutes, until the bottom edges and some parts of the top of the cookies are golden brown. Halfway through bake time, swap and rotate trays in the oven.
Transfer each baking sheet to a cooling rack and let cookies cool completely on the tray. This will ensure you get that perfect chewy cookie texture that makes these banana cream pie cookies so irresistible.
Store in an airtight container at room temperature for 1-2 days or freeze for up to 3 months.