Preheat the oven to 350°F.
Lightly grease two 9x5 inch loaf pans with butter, or line them with parchment paper.
In a large mixing bowl, whisk together the flour, baking powder, baking soda, salt, and pumpkin pie spice.
In a separate bowl, add the sourdough discard, brown sugar, melted butter or oil, eggs, and pumpkin puree. Whisk until smooth and well combined.
Pour the wet ingredients into the dry ingredients.
Stir gently until just combined. Do not overmix. A few small streaks of flour are better than overworking the batter.
Fold in the dried cranberries.
Divide the batter evenly between the two prepared loaf pans.
Smooth the tops with a spatula.
Bake for 55 to 60 minutes, or until a toothpick inserted into the center of each loaf comes out clean.
If the tops begin browning too quickly, loosely tent the pans with foil for the last 10 to 15 minutes of baking.
Let the loaves cool in the pans for about 10 minutes.
Carefully transfer the loaves to a wire rack and let them cool completely before slicing.
If adding the orange glaze, whisk the powdered sugar, orange juice, and orange peel together in a small bowl. Drizzle over the cooled loaves before serving.