Preheat oven to 350 degrees F. Line 8.5 x 4.5 inch loaf pan with parchment paper.
Mix dry ingredients together in a large bowl and set aside. (All-purpose flour, oat flour, baking soda, baking powder, cinnamon, cardamom, ginger, and salt.)
Whisk pumpkin puree, oil, eggs, sugar, and brown sugar together in another bowl until smooth. Then whisk in sourdough discard, vanilla, and molasses until smooth. Stir dry ingredients into wet, just until no flour streaks remaining.
Put batter into an 8.5 x 4 inch loaf pan that is lined with parchment paper. parchment lined loaf pan and bake for about 1 hour (check loaf at 45 minutes to see how it is progressing), until toothpick comes out clean.
Let bread completely cool in the pan on a wire rack.
Whisk powdered sugar into butter until smooth, then whisk in maple syrup and salt. Let sit for 5 minutes to thicken slightly. Whisk again, then drizzle onto cooled bread.