Spray the bottom of a 9 x 13 inch baking dish with non stick cooking spray.
Make the yellow cake according to directions on the box.
When it is done baking, remove from oven and poke holes all over the entire top of the cake with the other end of a wooden spoon. Do this while the cake is still hot. Pressing the holes about halfway through the baked cake.
Mix together the pineapple juice reserved from the crushed pineapple, sweetened condensed milk and cream of coconut together. Whisk until well stirred.
Spoon the mixture over the top of the cake trying to pour it into the holes.
Let the cake cool completely.
Top the cake with the well drained crushed pineapple.
In another bowl mix the sweetened whipped cream by beating the whipping cream and powdered sugar in a bowl until thick and it can stand on it's own.
Spread carefully over the crushed pineapple.
Top with shredded coconut.
Store in the fridge until ready to serve.
Notes
We store Pina Colada Cake in the fridge to help the mixture set up that was poured into all of the holes.