In a medium bowl, combine ½ cup of all-purpose flour, ¼ cup of granulated sugar, ¼ cup of brown sugar, and a pinch of salt. Pour in 4 tablespoons of melted unsalted butter, and mix until crumbly. Set aside.

In a large bowl, whisk together 2 cups of all-purpose flour, ½ teaspoon of salt, 1 teaspoon of baking powder, 1 teaspoon of baking soda, and 2 teaspoons of pumpkin pie spice. Set aside.

In another bowl, mix ½ cup of melted unsalted butter with ½ cup of brown sugar until smooth. Add 1 large egg, 2 teaspoons of vanilla extract, 1 cup of sourdough discard, and 1 cup of pumpkin puree. Stir until well combined.

Gently pour the wet mixture into the dry ingredients, stirring until just combined with a few flour streaks remaining.

Pour the batter into a greased 9x5 inch loaf pan, sprinkle the crumb topping on top, and bake at 350°F for about 60 minutes, or until a toothpick comes out clean.

Let sit in the pan for 10-15 minutes, then transfer to a wire rack to cool completely.