Preparation

• Preheat your oven to 350 degrees F. Grease a 9×13 inch cake pan with nonstick spray or rub with butter.
• Make the streusel: In a large bowl, whisk together 3 cups flour, 1 cup brown sugar, ½ cup granulated sugar, 1 teaspoon kosher salt, 1 tablespoon cinnamon, and 1 tablespoon pumpkin pie spice.
• Melt 1 cup butter in a medium bowl in the microwave. Pour into the larger bowl and stir the butter into the flour.
• Set aside the streusel mixture, ideally refrigerate it if you have room.
• For the cake: In a large bowl or stand mixer, whisk together 2 and ¼ cups flour, 1 and ½ cups granulated sugar, 1 tablespoon baking powder, ¾ teaspoon baking soda, ¾ teaspoon kosher salt, 1 tablespoon pumpkin pie spice, and 1 teaspoon cinnamon.
• Chop ½ cup softened butter into chunks and add it to the flour mixture.
• Use a spatula to scoop out half of the can of pumpkin puree and add it to the bowl with the flour and butter. Blend until moistened.
• In the bowl where the butter was melted, whisk together the remaining pumpkin, 4 eggs, ¼ cup vegetable oil, and 1 tablespoon vanilla.
• Add the egg mixture to the flour mixture in 3 additions, beating well between each addition.
• 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 batter on top and evenly distribute.
• Add another 1 cup streusel on top.
• Add the remaining batter and spread evenly.
• Spread another 2 cups of streusel on top of the cake.
• Bake the cake at 350 for 35 minutes.
• Quickly add the remaining streusel on top of the cake, focusing on areas where the cake has puffed.
• Bake for another 10-15 minutes. The cake is done when a toothpick inserted in the center comes out clean.
• Let the cake cool on a wire rack for at least 15-20 minutes before cutting.
• Make the icing: In a medium bowl, beat the softened butter until smooth.
• Mix in vanilla, kosher salt, milk, and powdered sugar, adjusting milk to reach desired consistency.
• Drizzle the icing over the cake.
• Serve warm; reheating individual servings in the microwave if desired.