Preheat your oven to 350°F (175°C) and grease a 9x13 inch baking pan.

In a mixing bowl, whisk together flour, brown sugar, granulated sugar, salt, cinnamon, and pumpkin pie spice. Add melted butter until it resembles wet sand, then refrigerate.

In another bowl, whisk flour, sugars, baking powder, baking soda, salt, and spices. Chop some butter into the mixture until crumb-like.

In a separate bowl, combine pumpkin puree, eggs, vegetable oil, and vanilla extract until smooth. Gradually mix into the dry ingredients to form a batter.

Layer two cups of batter in the pan, sprinkle a cup of streusel on top, repeat layers, finishing with batter.

Bake for 35 minutes, sprinkle remaining streusel, then bake for an additional 10-15 minutes until a toothpick comes out clean.

Cool in the pan for 15-20 minutes. Prepare icing by beating butter, vanilla, salt, milk, and powdered sugar until smooth.

Drizzle the icing over the cooled cake and let it set before serving.