Preheat the oven to 325 degrees F and grease a 9 inch square baking dish well, set aside.

Start by making the streusel topping by adding the flour, granulated sugar, brown sugar, and cinnamon to a medium bowl. Use a fork to whisk to combine. 

Add the melted butter and stir until fully incorporated. Set aside.

Make the cake by adding the flour, sugar, salt, baking powder, and baking soda to a large bowl. Whisk to combine.

Create a well in the center of the dry ingredients and add the eggs, sour cream, melted butter, milk, and vanilla. Stir to combine taking care to fully incorporate everything without over mixing. 

Add a little more than half of the cake batter to the prepared pan and spread it out evenly.

Remove 1 cup of the streusel topping and sprinkle it evenly over the first cake layer. 

Add the rest of the batter on top of the cinnamon streusel layer and spread it evenly in the pan.

Add the remaining streusel over the top of the cake. 

Bake for 45 to 50 minutes of until a toothpick inserted into the center of the cake comes out clean. 

Remove from the oven and allow the cake to rest for 30 minutes before serving. 

Serve warm or at room temperature.