Sterilise the jars: Fill a large pot with water and bring it to a boil. Boil the jars and lids for 10 minutes to sterilise. Carefully remove onto a clean towel. Cover with another clean towel. Then boil the rubber rings for 2-3 minutes. Just leave them in the hot water until you're ready to use them! (Instructions from WeckJars.com)
Prep: Preheat the oven to 360°F. Mix the apples with the cinnamon in a small bowl. Set aside.
Make the batter: Mix the flour, baking powder, sugar and gingerbread spice mix in a medium bowl. Add the eggs, melted butter, buttermilk and molasses to the bowl and mix until a smooth batter forms. Fold in the prepared apples and chopped walnuts.
Bake the cake: Evenly spoon the batter into the prepared jars. If you drop batter on the rim, wipe it clean. Bake the cake jars without the lid for 25-30 minutes, or until a toothpick inserted comes out clean.
Seal: As soon as you take the jars out of the oven, seal them with a rubber ring, a lid and the metal clamps (make sure your hands are very clean). Careful, the jars are very hot - use a clean dish towel to hold them!
If you work carefully and clean, the cake will keep for two weeks, as long as the seal remains unbroken.