Preheat the oven to 350 degrees F. Spray a 9 by13-inch cake pan with nonstick spray.
In a large bowl, add the cake mix, 1 cup evaporated milk, oil, and eggs. Using an electric hand mixer on medium speed, beat for 2 minutes until smooth. Pour the batter into the prepared pan and bake until a toothpick inserted in the middle of the cake comes out clean, 30 to 35 minutes. Let cool.
In a medium bowl, whisk together the sweetened condensed milk, remaining evaporated milk, and 1/4 cup cream. Using a fork, poke holes all over the cake. Pour the milk mixture evenly over the cake. Place in the refrigerator until the liquid absorbs into the cake, at least 1 hour or overnight.
When you are ready to serve, in a large bowl, add the remaining cream and vanilla. Beat with an electric hand mixer on high speed until the cream holds soft peaks.
Slice the cake and serve with a dollop of whipped cream and garnish with toasted coconut.