Toss the blueberries in the tablespoon of flour and set aside.

In the bowl of a mixer beat butter with sugar until mixed well.

Add in egg, vanilla, and banana, mix until combined.

Place flour, baking powder, and salt in a bowl and stir to combine.

Add half the flour mixture to the butter mixer then add half the buttermilk,

Then add the other half of the flour mixture, then the remaining buttermilk.

Stir in the blueberries.

Prepare the mason jar lids by spraying them with a baking spray or grease and flour them.

Place the jar lids on a baking sheet.

Place 1/4 cup batter into each lid.

Bake at 350° for 15 minutes.

Test the cakes with a toothpick, it should come out clean.

Let the cakes cool before removing them from the jar lids or serve them in the lids.