Preheat oven to 350 degrees. Grease a 9x13 inch pan.

In a large bowl, beat cake mix, half and half, oil and eggs on medium speed until smooth.

Pour the batter into the prepared pan and bake for 30-35 minutes, or until cake is golden brown. Cool completely.

Meanwhile, make the milk mixture by combining the sweetened condensed milk, coconut milk, half and half and vanilla in a medium bowl. Whisk until well combined.

Poke the cooled cake all over with a fork.

Pour half of the milk mixture over the cake and spread with a spatula to cover. Wait five minutes, or until most of the liquid is absorbed.

Pour the remaining milk mixture over the cake and spread to cover evenly.

Refrigerate the cake for at least 4 hours, or overnight.

To serve, top with whipped cream, toasted coconut and sliced bananas (if desired). Store leftover cake in the refrigerator.