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

Make the streusel: In a large bowl, whisk together the flour, brown sugar, granulated sugar, salt, cinnamon, and pumpkin pie spice. Melt the butter in a medium bowl and pour it into the dry ingredients. Stir until the mixture resembles wet sand with big chunks. Set aside, and place it in the fridge if space allows.

In a large bowl or stand mixer, combine the flour, granulated sugar, baking powder, baking soda, salt, pumpkin pie spice, and cinnamon.

Chop the softened butter into chunks and add it to the dry mixture. Mix until the butter is incorporated.

Scoop half of the pumpkin puree into the flour mixture. Blend with a mixer until it forms a cohesive batter. Add more pumpkin if necessary to help it come together.

In the same bowl used for the melted butter, whisk together the remaining pumpkin puree, eggs, vegetable oil, and vanilla. Add this to the flour mixture in three additions, mixing for 20 seconds after each addition. Beat for an additional minute until light and fluffy.

Spread 2 cups of batter in the bottom of your prepared pan. Sprinkle 1 cup of streusel over the top. Spread another 2 cups of batter, followed by another 1 cup of streusel. Add the rest of the batter and top with 2 cups of the remaining streusel.

Bake for 35 minutes. Quickly sprinkle the remaining streusel over the top, then return to the oven for an additional 10-15 minutes, until a toothpick inserted in the center comes out clean.

Let the cake cool for 15-20 minutes on a wire rack before icing it.

In a medium bowl, beat the butter until smooth. Add vanilla, salt, milk, and powdered sugar, mixing until smooth. Drizzle over the cake, either on the whole cake or each individual slice.