For the bananas:
Place sliced bananas in a microwave safe bowl. Cover the bowl with plastic wrap and make several slits in the wrap. This will act as steam vents. Microwave on high until the bananas are soft and have released liquid, about 2-3 minutes. Transfer the bananas to a fine mesh strainer set over a medium bowl and drain, stirring and mashing the bananas to release the liquid. You are going to end up with a bit less than ½ cup of liquid, and about ¾ cup of banana puree. Transfer the banana puree to a small bowl and set aside.
Transfer the reserved banana liquid to a small saucepan and place over medium-high heat. Cook until the liquid is syrupy and reduced to about 1 oz. (2 tablespoons), about 3-4 minutes. Remove the pan from the heat and allow the liquid to cool.
For the cornstarch slurry:
To a small bowl add the cornstarch and milk. Stir until combined and set aside.
Make the ice cream base:
Prepare a large bowl with ice water and place an open 1 gallon Ziploc bag inside and set aside.
To a medium saucepan add the milk, heavy cream, sugar, light corn syrup and vanilla extract. Stir until sugar is dissolved and bring mixture to a simmer over medium/high heat. Remove from heat and add the cornstarch slurry. Return mixture to heat and whisking quickly (and entire time) allow the cornstarch to cook and the mixture to thicken slightly, about 4 minutes. Remove from heat and add the banana liqueur, reduced banana syrup, and mashed bananas. Stir until bananas are mostly dissolved.
Pour the mixture into the Ziploc bag set over an ice bath. Close the Ziploc bag and allow the mixture to cool completely. Once the mixture has completely cooled, please it in the refrigerator and allow it steep for at least 4 hours, or preferably overnight.
Freeze the ice cream and add mix ins:
Remove the ice cream base from the refrigerator and strain, pressing on the solids to extract as much of that steeped liquid as you can. Discard the solids and freeze the ice cream according to manufacturer’s directions. Once Ice cream is frozen, fold in the Nilla Wafer pieces and banana slices. Place in an airtight container with a tight fitting lid and place the ice cream in the freezer for a few hours to harden completely.