Preheat the oven to 350 degrees F. Grease a 9×13 inch cake pan with nonstick spray or butter.

In a large bowl, whisk together 3 cups flour, 1 cup brown sugar, 1/2 cup granulated sugar, 1 teaspoon kosher salt, 1 tablespoon cinnamon, and 1 tablespoon pumpkin pie spice.

Melt 1 cup butter in a medium bowl. Pour into the larger bowl and stir the butter into the flour. Set aside.

In a large bowl or stand mixer, whisk together 2 & 1/4 cups flour, 1 & 1/2 cups granulated sugar, 1 tablespoon baking powder, 3/4 teaspoon baking soda, 3/4 teaspoon kosher salt, 1 tablespoon pumpkin pie spice, and 1 teaspoon cinnamon.

Chop 1/2 cup butter into chunks and add it to the flour mixture.

Add about half the can of pumpkin puree to the bowl with the flour and butter. Blend until the mixture comes together in a ball.

In the medium bowl that you melted butter in, add the remaining pumpkin, whisk in 4 eggs, 1/4 cup vegetable oil, and 1 tablespoon vanilla.

Add the egg mixture to the flour mixture in 3 additions, beating for about 20 seconds after each one. Beat for another 1 minute until the batter is light and fluffy.

Spread 2 cups of batter into the bottom of the prepared cake pan.

Sprinkle 1 cup of streusel evenly over the top.

Spread another 2 cups of batter on top.

Add another 1 cup streusel on top.

Add the rest of the batter and spread evenly.

Evenly spread another 2 cups of streusel on top of the cake.

Bake the cake at 350 for 35 minutes.

Remove the cake from the oven and sprinkle all the remaining streusel on top.

Bake for another 10-15 minutes. The total bake time should be about 45-50 minutes. Test for doneness with a toothpick.

Let the cake cool on a wire rack for at least 15-20 minutes before cutting.

In a medium bowl, beat 1/4 cup butter until smooth. Add 1 teaspoon vanilla, 1/2 teaspoon kosher salt, 3 tablespoons milk, and 2 cups powdered sugar. Beat until very smooth.

Drizzle the icing over the cake.