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

In a large bowl, whisk together the streusel ingredients: 3 cups of 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 of butter and pour it into the larger bowl with the dry ingredients. Stir until it resembles wet sand. Set aside, and if space allows, place it in the fridge.

In a large bowl or stand mixer, whisk together 2 and 1/4 cups of flour, 1 and 1/2 cups 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 of softened butter into chunks and add it to the flour mixture.

Scoop about half of the can of pumpkin puree into the bowl and mix using the paddle attachment or electric beaters. Avoid overmixing.

In the medium bowl used for the butter, add the remainder of the pumpkin, whisk in 4 eggs, 1/4 cup vegetable oil, and 1 tablespoon vanilla extract until well blended.

Gradually add the egg mixture into the flour mixture in three additions, mixing for about 20 seconds after each addition. Beat for another minute until the batter is light and fluffy.

Spread 2 cups of batter into the prepared cake pan and sprinkle 1 cup of streusel evenly over the top.

Add another 2 cups of batter, followed by 1 cup streusel, then the rest of the batter. Top with the remaining 2 cups of streusel.

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

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

In a medium bowl, beat 1/4 cup of butter until smooth. Add 1 teaspoon vanilla, 1/2 teaspoon kosher salt, 3 tablespoons milk, and 2 cups powdered sugar. Blend until smooth, adjusting with milk if necessary.

Drizzle the icing over the cooled cake before serving.