Step 1

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

Step 2

Make the streusel: In a large bowl, whisk together 3 cup flour, 1 cup brown sugar, 1/2 cup granulated sugar, 1 teaspoon salt, and 2 tablespoons cinnamon.

Step 3

Melt 1 cup butter in a small bowl in the microwave. Pour into the larger bowl and stir the butter into the flour. You should end up with a bowl of what looks like wet sand, with lots of big chunks. Don't try to smooth it out. See photo.

Step 4

For the cake: In a large bowl or stand mixer, whisk together 2 and 1/4 cups flour, 1 and 1/4 cups sugar, 1 tablespoon baking powder, 3/4 teaspoon baking soda, and 3/4 teaspoon salt.

Step 5

Chop 3/4 cup softened butter into chunks. You want the butter to sit out of the fridge for several minutes to that it's not rock-hard, but don't let it soften so much that it's completely creamy.

Step 6

Add the chopped butter and 1/2 cup sour cream to the flour mixture. Use the paddle attachment (or electic beaters) to blend the butter in. Eventually the butter will moisten the flour and it will all come together in a ball. Scrape the bottom and sides of the bowl as necessary. Don't over mix, just beat until all the butter is incorporated.

Step 7

In another large bowl, whisk together 4 eggs, 1 cup sour cream, and 1 tablespoon vanilla. Beat well until the eggs are well blended.

Step 8

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

Step 9

Spread 2 cups of batter into the bottom of your prepared cake pan. Sprinkle 1 cup of streusel evenly over the top, breaking up any too-large pieces with your hands.

Step 10

Spread another 2 cups batter on top and spread it around as best you can.

Step 11

Add another 1 cup streusel on top.

Step 12

Add the rest of the batter and spread evenly.

Step 13

Evenly spread another 2 cups of streusel on top of the cake. Do NOT add all the remaining streusel! There will be some left over. Spread the remaining streusel on a baking sheet to dry out a little bit.

Step 14

Bake the cake at 350 for 25 minutes.

Step 15

Do this next part fast. Remove the cake from the oven and shut the oven door. Use your hands to sprinkle all the remaining streusel on top of the cake, focusing on any areas where the cake batter has puffed up from the center. Move quickly! Get the cake back in the oven as soon as you can, and keep the oven door shut as much as possible.

Step 16

Bake for another 20-25 minutes.* The total bake time for the cake should be about 45-50 minutes, depending on your oven and whether you use a glass or metal pan. Test the cake with a toothpick. It is done when a toothpick inserted in the center comes out with no wet batter on it. The cake should not wobble around at all when you shake the pan.

Step 17

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

Step 18

Make the icing: In a medium bowl, beat 1/4 cup butter until smooth. (I actually did it by hand with a whisk. You can do this if your butter is ultra soft.)

Step 19

Add 1 teaspoon vanilla, 1/2 teaspoon salt, 1/4 cup milk, and 2 cups powdered sugar. Beat with a mixer or by hand until very smooth.

Step 20

Drizzle the icing over the cake. You can either drizzle it over the whole cake or drizzle each individual serving. I like to drizzle about half the icing over the whole cake, and then save the rest of drizzling over each serving.

Step 21

The cake is best served warm! Zap individual servings in the microwave for 10-20 seconds if you are serving after the cake has cooled.

Step 22

This cake will keep well covered on the counter for 2-3 days. After that, put it in the fridge.