In a medium-sized bowl, combine sweetened condensed milk and milk and beat on medium speed until the milks are well mixed. Add the instant pudding to the milks and beat until well combined. Pudding must be refrigerated for 3-4 hours until completely firm.
Put your mixing bowl and wire whisk in the freezer to help it get very cold. This is optional, but something I usually do.
Beat heavy whipping cream on medium-high speed. Slowly added powdered sugar, increasing speed to high and beat until stiff peaks form.
Slowly fold whipped cream into pudding until combined.
Use a Ziploc bag to crush Nilla Wafers. In a 9-inch square pan, put down a layer of parchment paper on the bottom of the pan. Sprinkle the bottom layer with crushed Nilla Wafers.
Slice bananas and place a layer of sliced bananas over the wafer. Pour half the pudding in the pan and gently spread over the bananas. Sprinkle another layer of wafers and bananas and top with remaining pudding. Sprinkle the top with any leftover wafers.