Preheat oven to 350F and spray an 8-inch or 9-inch baking pan with non-stick cooking spray. Line with parchment paper for easy removal if desired, and spray with non-stick cooking spray. (For the thickest bars, use an 8-inch pan, for medium-thick bars, use a 9-inch baking pan, and if you want thinner bars, you can also use a 9x13 pan - Can also halve recipe and transfer cookie dough to a 9x5 loaf pan or an 8-inch baking pan for thinner snickerdoodle bars).
In a medium bowl, whisk together flour, baking powder, and salt.
In a separate large bowl, using a mixer, mix together the softened vegan butter and 1 ½ cups sugar. Add the applesauce and vanilla extract to the butter/sugar mixture and mix until well combined.
In three small batches, add the dry ingredients to the wet ingredients and stir until incorporated.
Spread the snickerdoodle cookie dough in the prepared baking dish (dough will be very sticky) and then top it with the cinnamon sugar mixture.
Bake for 25-30 minutes until bars are baked and the tops are not shiny and will have a light imprint if you touch the top with your finger. If they are still wet, bake them a little more. If you're baking these in a 9x13 pan, bake 20-25 minutes. Make sure to not overbake bars to have a soft and chewy texture.
Let the bars cool completely before cutting them.