Preheat your oven to 350 degrees F. Grease a 9x13 inch cake pan with nonstick spray or butter.

Make the streusel: In a large bowl, whisk together flour, brown sugar, granulated sugar, salt, cinnamon, and pumpkin pie spice. Melt 1 cup of butter and stir it into the flour mixture until it resembles wet sand. Set aside.

Prepare the cake: In another bowl, whisk together flour, sugar, baking powder, baking soda, salt, and spices. Add chunks of cooled butter and half a can of pumpkin puree, mixing until fully incorporated.

In a medium bowl, whisk remaining pumpkin, eggs, oil, and vanilla extract until well blended. Gradually add this mixture to the dry ingredients in three additions, beating for about 20 seconds after each one.

Spread half of the batter into the prepared cake pan and sprinkle 1 cup of streusel over the top. Follow with another layer of batter and more streusel. Spread the remaining batter on top, finishing with the streusel.

Bake for 35 minutes. Quickly add any leftover streusel and return to the oven. Bake for another 10-15 minutes, testing with a toothpick for doneness.

Let the cake cool on a wire rack before icing it.

Beat the butter until smooth, then add vanilla, salt, milk, and powdered sugar. Mix until smooth and drizzle over the cake.