Cinnamon Streusel Coffee Cake

Firstly, preheat your oven to the optimal temperature of 350 degrees F (175 degrees C). Next, lightly coat a 9x13-inch baking dish with oil or cooking spray and set it aside for later use.

Prepare the cinnamon layer by mixing together brown sugar, flour, and a pinch of warm cinnamon in a small bowl until they are thoroughly blended together; set it aside.

Create the streusel topping by combining brown sugar, flour, a pinch of warm cinnamon, and a small amount of salt in a small bowl. Add the cold butter to this mixture and use a fork to stir it until the ingredients form a crumbly texture; set it aside.

In another bowl, whisk together flour, baking powder, and a small amount of salt until they are well combined.

Using a stand mixer fitted with the paddle attachment, cream together sugar and butter on medium speed until they become light and fluffy. Scrape the sides of the bowl, then reduce the mixer's speed to low and beat in eggs until they are fully incorporated. Gradually add the flour mixture and milk, mixing until well combined. Add a spoonful of sour cream and vanilla extract, then beat the mixture for 30 seconds.

Pour half of the batter into the prepared baking dish. Sprinkle the cinnamon layer evenly over the batter, then pour the remaining batter over top. Spread the streusel topping evenly over the cake, pressing it gently so that it adheres to the batter.

Finally, bake the cake in the preheated oven until a toothpick inserted into its center comes out clean, taking around 40 to 50 minutes. Remove the cake from the oven and let it cool completely before serving, which should take around 30 minutes.