To begin, you're going to make your cookies. Preheat the oven to 325°F. Line cookie sheets with parchment paper and set them aside. In a medium bowl, or the bowl of a food processor fitted with the steel blade attachment, add the flour, baking powder, baking soda, and brown sugar and whisk or pulse to combine. Add the butter, egg, and vanilla, and beat or process until well-combined. Add the milk, and beat or process until the dough clumps.
Pipe an tablespoon amount through a pastry bag fitted with a plain piping tip (for more consistent cookie sizing) about 1 inch apart on the prepared baking sheets. The, with wet fingers, gently flatten the top of each cookie. Place the baking sheets in your preheated oven and bake for 15 - 17 minutes, or until the cookies are uniformly golden brown in color. Allow the cookies to cool completely on the baking sheets.
While the cookies are cooling, it's time to mix up your pudding! In a mixing bowl, beat cream cheese with sweetened condensed milk until smooth. Add in pudding mix and milk. Beat for several minutes, until it reaches it good, thick consistency. Beat up your whipped cream or use your non-dairy whipped topping and fold it into the pudding mixture to make it light and fluffy.
To assemble, start with a 9x13 baking dish and line the bottom with half of your cooled Nilla Wafer cookies. Top that layer with sliced banana and then your fluffy pudding mixture on top of that. Smooth that out and then top with your remaining cookies. Cover your dish and refrigerate for at least 4 hours to let it set fully.