Mix gelatin and cold water together and set aside.
Heat cream, sugar, and zest, on the stove or in the microwave, until the mix is simmering and sugar is dissolved. Stir in the gelatin mixture, followed by the buttermilk.
Divide mixture between 6-8 jars, juice glasses, ramekins, small bowls, etc. and chill at least 5 hours. Once firmly set, top with fruit & jam. Serve chilled.
For a layer of jam in the center of the dessert, fill the jar halfway with the cream mixture. Chill about 1 hour, until mostly set. Gently spread the jam on top of the chilled panna cotta, then pour another layer of cream mixture on top of the jam.