Add the cold heavy cream, granulated sugar, vanilla and salt. Use a small spoon to stir until the sugar and heavy cream are mixed well and you can barely hear the sugar on the bottom of the mason jar. (It is very important that the heavy cream is cold to achieve the desired thickness)

Place the lid firmly and securely on the mason jar. Shake the jar for about 5 minutes, until the ice cream base has thickened. (This will help reduce any possible spills)

Place the mason jar in the freezer for 3 hours. If you are using any of the add-ins, especially the sprinkles and mini chocolate chips, wait for about 1 hour before you remove the lid and add the add-ins. In my experience the sprinkles and mini chocolate chips tend to sink to the bottom. Waiting until the ice cream begins to set will help keep the add-ins from sinking to the bottom. Use a spoon to stir in the add-ins. Return the jars to the freezer.

Once the ice cream is solidly set, remove the jar from the freezer and enjoy.