Preheat the oven to 350°F. Line an 8x8-inch baking pan with parchment paper.
To make the dough: In the bowl of a stand mixer fitted with the paddle attachment, add the butter, cane sugar, powdered sugar, and vanilla bean paste. Mix on low until combined and there are no butter chunks.
Add the egg and sour cream and mix on low for a few rotations. Add the egg and sour cream and mix on low for a few rotations. Then add the dry ingredients: flour, baking powder, salt, and cinnamon and mix to combine into a cookie dough.
Transfer the dough to the prepared baking pan and spread it out evenly, either using a spatula or your hands.
Bake for 25 to 27 minutes or until a the middle looks set and the edges look lightly golden brown. Allow to cool completely in the baking pan.
To make the frosting: In the bowl of a stand mixer fitted with the paddle attachment, add the butter, powdered sugar, vanilla extract, and beet powder. Mix on low and add in 1 to 2 tablespoons of milk as needed to create a smooth and creamy frosting. Be sure to scrape down the sides of the bowl party way through mixing to ensure everything is combined.
Transfer the frosting to two piping bags, one with Ateco tip #846 and the other with Ateco tip #21.
Pipe rosettes on the top of the bars with Ateco tip #846. Fill in with rosettes and dollops with Ateco tip #21. Top with nonpareils.
Cut into 9 bars and enjoy. Store in an airtight container in the fridge for up to 5 days.