Preheat oven to 325. Lightly grease a 13 x 9 cake pan.
Measure out 1/2 c cake mix and set aside.
Place the remaining cake mix, macadamias, melted butter and 1 egg in a large bowl. Beat at low speed for 2 minutes. Batter should come together into a ball.
With your fingertips, pat dough into an even layer on the bottom of the prepared pan.
In a glass measuring cup, microwave white chocolate on high for 1 minute. Stir until smooth.
Place cream cheese in the same mixing bowl you used for the crust mixture. Beat on low speed until smooth. Beat in reserved cake mix. Beat in white chocolate and condensed milk until just combined, about 30 seconds, scraping down sides as needed.
Beat in eggs, one at a time.
Mix in bananas and vanilla.
Pour over crust and smooth with rubber spatula.
Bake until it looks shiny and golden brown and the center no longer jiggles when you shake the pan, about 45 to 50 minutes.
Remove from oven, let cool for about 30 minutes. Cover tightly with plastic wrap or "Press-N-Seal" and refrigerate for at least an hour, or overnight.