Combine all ingredients except for the buttermilk into in a large sauce pan. Heat just until the sugar is dissolved. Remove and allow to cool completely. Stir in the buttermilk and then place into a freezer safe container. Cover and freeze for 1 hour. Stir every hour for 3 hours.
For the Crust:
Mix together in a large bowl your graham cracker crumbs, pistachio crumbs, butter and sugar. Press into a parchment lined 8x8 pan. Place in freezer for just 10-15 minutes until very firm. Then gently spread your sherbet onto the crust. Put it back into the freezer for another 30 minutes until firm. Melt your chocolate in a double broiler on medium to low heat stirring until the chocolate is completely melted. Immediately pour over the pineapple sherbet layer-spread to all four corners. Wrap your pan tightly in plastic wrap and return to the freezer for another 30 minutes. Cut and serve cold on a nice hot summer day!
Recipe by Kitchen Belleicious at https://kitchenbelleicious.com/2014/07/17/frozen-chocolate-covered-pineapple-bars-with-pistachio-graham-cracker-crust/