Melt the white chocolate and condensed milk together in the slow cooker on high for around 30-45 mins or until smooth and melted together. Leave the lid off.
Stir every five to ten minutes.
Once the mixture is smooth and looks quite thick, add the sifted icing sugar and mix well until it is all combined.
Pour half the fudge mixture into a loaf tin (or whatever you would like to use) lined with baking paper.
Scatter half the pistachios on top. Then pour the rest of the fudge in.
Top with the remaining pistachios and scatter the freeze dried raspberry pieces on top.
Press the pistachios and raspberry pieces in gently, then chill the fudge in the fridge until set.
This took three to four hours in my fridge, but I left it overnight.
Cut into squares and serve.