Preheat oven to 180 C (355 F) and line a baking tray with baking paper.
Melt butter and peanut butter together in a pot on the stove (low heat). Stir constantly to avoid burning.
Once melted, put peanut butter mixture into a mixing bowl.
Add mashed banana and mix.
Add flour and mix until it forms a soft dough.
Roll tablespoon sized amounts into balls and place on prepared baking tray, evenly spaced.
Flatten them gently, then carefully press a finger into the middle of each to make small dents.
Put a little bit of jam into each one.
Bake for approximately 16 minutes, or until the edges are just starting to turn golden brown.
Allow to cool at room temperature, then store in an airtight container in the fridge for a few days.