Heat oven to 350F. Line a baking sheet with parchment paper.

In a medium mixing bowl, whisk the flour, baking powder, cornstarch, salt, baking soda and cinnamon until combined. Set aside.

In the (separate) bowl of a stand mixer, cream the butter and brown sugar together on medium-high speed until light and fluffy, about 1 minute. Add peanut butter, egg, banana, and vanilla, and continue mixing on medium speed until combined, scraping down the sides of the bowl once if needed. Fold in the dry ingredients and mix until just combined.

Measure out a rounded tablespoon-full of dough, roll it into a ball, then place on the baking sheet. Use a fork to press down the top of the ball and make a criss-cross pattern. Sprinkle with a pinch of cane sugar, if desired. Repeat with remaining dough.

Bake for 8-10 minutes or until slightly golden around the edges. Cool for 10 minutes on baking sheet, then transfer to a wire rack to cool completely.

Serve immediately or store in a sealed container for up to 1 week.