Coconut Tres Leches Cake

Place a rack in the center of the oven and preheat the oven to 350 degrees.
Lightly spray a 9x13-inch baking dish with cooking spray. Set the baking dish aside. Make the boxed cake mix or yellow cake according to box or recipe instructions (you'll typically need water, eggs, and oil, as directed in mix package). Scrape batter into the prepared pan. Bake according to recipe/box directions. Remove the cake from the oven and place it on a wire rack to cool completely, 1 hour.
Meanwhile, make the milk syrup: in a blender, combine the cream of coconut, evaporated milk, cream, and vanilla and process until smooth.
Pierce the cooled cake all over the top with the tines of a fork or a thin wooden skewer. We are talking all over! The more pokes, the more the syrup will soak into the cake. Using a large spoon or ladle, spoon some of the milk syrup over the cake. Let the syrup soak into the cake, then continue spooning the syrup on top until all of it has been used up. When you have finished, not all of the syrup will be completely absorbed and might be pooling on the top but that's ok because it will absorb as it refrigerates. Cover the cake loosely with plastic wrap and refrigerate until all of the syrup is absorbed, 2 hours.
Cut the bananas, if using, crosswise into 1/4-inch slices. Slice the cake and serve it with sliced bananas, sweetened cream and toasted coconut, if desired.