Preheat your oven to 400 degrees. Line a large baking sheet with parchment paper.
In a large bowl, combine flour, salt, baking soda, baking powder, and cocoa powder.
Add butter. Use your fingers to mix and “smush” the butter, working it into the flour mixture.
Complete the smushing until you have sand-like texture. Set aside.
In a large liquid measuring cup, add 1 cup sourdough starter discard, vanilla, and brown sugar. Stir until brown sugar is fully dissolved.
Add to flour mixture, adding additional starter as needed to bring the flour together (up to about ⅓ cup).
Once combined, gently fold in the bananas and walnuts. The dough will be moist.
Cut the dough into four equal pieces. Form these pieces into discs and place on lined baking sheets. Slice into 6-8 pie pieces.
Bake for 15-18 minutes, until just firm to the touch.
Once cooled, feel free to add a chocolate drizzle for an extra touch of sweetness or beauty, but we thought they were great on their own!