Make the vanilla pudding:

If you are using store-bought pudding then you don't need to prepare the pudding and you can make these banana pudding parfaits in minutes. If you are making vanilla pudding using a box mix, follow the instructions on the box.

To make homemade vanilla pudding:

1. In a medium saucepan, whisk together sugar, cornstarch, salt, and egg yolks until well blended. Whisk in the milk and heat over medium heat, stirring often, about 5-8 minutes.
2. Once the mixture starts to bubble, turn the heat down to low and continue cooking until thickened, whisking often, about 1-2 minutes more. Note that pudding will be pourable but will continue to thicken more as it cools.
3. Remove from heat and immediately whisk in the butter and vanilla, stirring until smooth.
4. If you notice any lumps, pass the pudding through a fine-mesh sieve over a large heatproof bowl to remove any lumps. Skip this if you don’t notice any lumps.
5. Prepare a large bowl with some water and ice to make an ice bath. Place the saucepan directly into the ice bath, stirring occasionally, until the pudding reaches room temperature, about 30 minutes.
6. Cover and refrigerate until the pudding has chilled through completely, at least 4 hours (up to 2 days).

Assemble the banana pudding:

1. Add a large dollop of pudding into the bottom of each parfait cup.
2. Top with a layer of wafer cookie pieces and a layer of sliced bananas.
3. Repeat these layers until you reach close to the top, ending with a final layer of pudding.
4. Finish each pudding with whipped cream and some crushed or crumbled wafer cookies.