Preheat the oven to 350°F (175°C). Grease a loaf pan or line it with parchment paper.
In a large bowl, combine the mashed banana, pumpkin puree, active starter or discard, melted butter, sugar, eggs, and vanilla. Mix until smooth.
In a separate bowl, whisk together the flour, baking soda, baking powder, pumpkin spice, and salt.
Mix in any add ins such as: raisins, cranberries, chocolate chips, or nuts.
Gradually add the dry ingredients to the wet mixture, stirring until just combined. Fold in any optional nuts or chocolate chips.
Pour the batter into the prepared loaf pan and smooth the top.
Bake for 55-70 minutes, or until a toothpick inserted into the center comes out clean.
Allow to cool in the pan for about 10 minutes, then transfer to a wire rack to cool completely.
Enjoy your delicious sourdough pumpkin banana bread!