No it is not necessary, you can use cold milk to prepare the mousse. However, you have to beat it with an electric mixer for about 3-4 minutes for the mousse to reach the right texture. Furthermore, this delicious mix can be used to decorate the Heart Cake or to fill delicacies like muffins. Preparing these desserts is very easy, you only have to follow the recipe that S.Martino added in the mousse page to delight your friends and family.