Preheat oven to 325 degrees F. Liberally spray a mini muffin tin with non-stick cooking spray.
Cream together sugar and butter. Add egg and vanilla, mix again, then add the sour cream, salt and soda. Add flour and beat until smooth.
Scoop out 1 TBSP of dough into each muffin cup. I use a cookie scoop- it makes this process so fast and I love that all the cookies are uniform! You'll have enough dough to make 24 cookie cups, plus about 6 more cookies. I just baked these additional cookies like normal on a cookie sheet. You'll crumble 1 to use for topping later on.
Bake for 17-18 minutes. Let cookies stand for 1-2 minutes after taking them out of the oven. Spray the round side of a 1 tsp measuring spoon with non-stick spray. Press down into the center of each cookie to create a well. Let cool completely- if you need to hurry this process, feel free to stick the pan in the freezer for 20 minutes.
While the cookies are cooling, you can mix up the banana cream pie filling. Whisk together the box of dry pudding mix and the milk. Add in the whipped topping and stir gently until combined. Transfer to a pastry bag or a ziplock bag and store in the fridge until the cookies are fully cool.
Take cookies out of muffin tin- I just slid the tip of a knife down 1 side and they popped right out.
Pipe banana cream into each cup and top with a slice of banana. Sprinkle with a small amount of cookie crumbles.
Store in the refrigerator. Cookies can be completely made and assembled up to 8-12 hours ahead of time. If any longer, make cookies and banana cream, then assemble just prior to serving.