Preheat your oven to 350°F (175°C). Grease the inside of each canning jar and set them aside.

In a mixing bowl, mash the ripe bananas until smooth.

In a separate bowl, whisk together the melted butter, granulated sugar, brown sugar, egg, and vanilla extract until well combined.

In another bowl, sift together the flour, baking soda, baking powder, salt, ground cinnamon, and any optional spices.

Gradually add the dry ingredients to the wet ingredients, stirring until just combined. Be careful not to overmix.

If desired, fold in chopped walnuts or chocolate chips into the batter.

Divide the batter evenly among the greased canning jars, filling each jar about halfway.

Place the jars on a baking sheet and bake in the preheated oven for approximately 25-30 minutes, or until a toothpick inserted into the center of each jar comes out clean.

Remove the jars from the oven and allow them to cool completely before sealing with the lids.