Prepare the cake:
Preheat the oven to 350°F (175°C). Grease and flour a 9×13-inch baking dish or line it with parchment paper for easy removal.

Mix the batter:
In a large bowl, combine the yellow cake mix and pistachio pudding mix. Add the vegetable oil, eggs, sour cream, crushed pineapple, shredded coconut, and chopped pistachios. Stir well to combine, ensuring everything is fully incorporated.

Bake the cake:
Pour the batter into the prepared baking dish and smooth the top with a spatula. Bake in the preheated oven for 30-35 minutes or until a toothpick inserted into the center comes out clean. Let the cake cool completely in the pan on a wire rack.

Make the frosting:
While the cake is cooling, prepare the frosting. In a large mixing bowl, beat the softened cream cheese with a hand mixer until smooth and creamy. Add the heavy cream and vanilla extract, and beat until fluffy. Gradually add powdered sugar and continue beating until the frosting is light and smooth.

Frost the cake:
Once the cake is completely cooled, spread the frosting evenly over the top using a spatula.

Garnish and serve:
Sprinkle the top of the frosted cake with shredded coconut and the reserved chopped pistachios for a tropical touch. Optionally, you can add a few pineapple slices or maraschino cherries for extra flair.

Chill and serve:
For the best texture, chill the cake in the fridge for about an hour before slicing and serving. Enjoy the tropical, nutty flavors in every bite!