In a medium sauce pan, cook the frozen raspberries over medium heat. As they soften, use a potato masher or a fork to break up the raspberries to release the juices. Allow the berries to simmer on low for about 15 minutes to thicken and allow the water to evaporate. The berry mixture should coat a spoon when it's thickened a little. If you need to, you can add a tablespoon of sifted cornstarch (while the mixture is cooking), to help thicken it.
Once the berries have cooked through and juice has thickened a little, pour the berries into a fine-mesh sieve that is set over a bowl. Push the juices through to remove the seeds. You'll use about 3/4 cup of the seedless juice but don't throw the rest away. Save it in an airtight container in case you need to thin your mixture later.
In a microwave safe bowl, pour the hot raspberry puree over the white chocolate chips. Stir until the white chocolate chips melt. If needed, microwave for 30 seconds to melt the chips completely. Stir until smooth.
In a separate bowl, crush the freeze-dried raspberries into a fine crumb. Push through a fine-mesh sieve to remove the seeds. Discard the seeds and add the raspberry powder to the ganache. Stir until blended. This should start to thicken the mixture.
Allow to cool to room temperature before adding to the cake. The ganache will thicken as it cools. The texture of the raspberry ganache should be thick, but easily spreadable. If it's too thin, refrigerate it for about 20 minutes or so to set more. To thicken even more, add additional freeze dried raspberry powder.