Bake the white cake according to the directions on the package in a 9x13 baking pan. Cool the cake completely and then cut into small cubes. Portion the cake cubes into 32 2-ounce plastic cups, filling approximately ⅔ full. Set remaining cake cubes aside.
In a mixing bowl, whisk together the sweetened condensed milk, evaporated milk, whole milk, and vanilla extract until well combined.
Use a squeeze bottle or a spoon to pour the milk mixture over the cake cubes to soak the cake. Add the additional cake cubes or crumbs to fill the cups ⅔ to ¾ full. Gently press the cake down to soak up the milk and create an even layer of cake.
In a separate mixing bowl, whip the heavy cream, powdered sugar and vanilla extract until stiff peaks form. Fill a piping bag with the whipped cream and pipe it onto the dessert cups. Use an offset spatula to spread the whipped cream into an even layer. If desired, add a sprinkle of cinnamon.
Seal the cups with a lid and chill in the refrigerator overnight. Store the dessert cups in the refrigerator for up to 3 days.