No, it's best to leave the Panna Cotta to cool at room temperature and then leave it to set in the fridge. Setting the Panna Cotta in the freezer causes it to set unevenly, with the outside setting quicker than the inside, which can negatively affect the texture. Once set completely in the fridge, the Panna Cotta can be transferred to the freezer to be stored if you're not planning on eating it within 2 days.