Combine brown sugar, flour, and a pinch of salt. Cut in cold butter until the mixture resembles coarse crumbs. Chill the streusel while preparing the bread batter.

Preheat oven to 350°F (175°C) and line a loaf pan with parchment paper.

In a mixing bowl, blend pumpkin puree, vegetable oil, granulated sugar, brown sugar, eggs, and sour cream until smooth.

In another bowl, whisk together flour, baking soda, baking powder, salt, and spices. Gradually fold into the wet ingredients.

Fold half the streusel into the batter, pour into the loaf pan, and top with remaining streusel.

Bake for approximately 1 hour and 10 minutes, checking doneness with a toothpick.

Remove from oven and cool in the pan for 10-15 minutes before transferring to a wire rack.