Preheat oven to 350 degrees F. and spray baking jars of choice with non-stick cooking spray.
Place cake mix, oil, sour cream, eggs, and pudding mix into the bowl of a stand or electric mixer, beating until well combined, about 1 minute.
Place flour, brown sugar, cinnamon, and salt into a medium bowl, mixing to combine. Cut cold butter into small cubes, add to flour mixture and use a pastry cutter or a fork and cut butter into mixture until well combined and crumbly. Takes a good 5 minutes.
Depending on the size of jar you use, this step will be different for every size. For the tiny jars I used, I placed about 2 tablespoons cake mix into the bottom, topped with 2 tablespoons cinnamon mix and topped with another 1 tablespoon of cake mix. No matter what size of jar you use, only fill it 1/2 full or you'll end up slicing off the top that bakes over the top. Use your best judgement according to the size jar you are using. Layer cake mix and cinnamon topping until you reach 1/2 full of your jar.
For my tiny jars, I baked them for 19 minutes and they were perfect. If using larger jars just keep a close eye on them after 20 minutes of baking. Carefully remove hot jars from oven, let cool then close with lids. Find some cute tags and wrap around top with a ribbon.